Why would the assumption be that acknowledging the existence of Jesus makes you Christian? And how is not being Christian weakening my claim?

Non-Christian sources used to study and establish the historicity of Jesus include the c. first century Jewish historian Josephus and Roman historian Tacitus. These sources are compared to Christian sources, such as the Pauline letters and synoptic gospels, and are usually independent of each other; that is, the Jewish sources do not draw upon the Roman sources. Similarities and differences between these sources are used in the authentication process.[82][83][84][85] From these two independent sources alone, certain facts about Jesus can be adduced: that he existed, his personal name was Jesus, he was called a messiah, he had a brother named James, he won over Jews and gentiles, Jewish leaders had unfavorable opinions of him, Pontius Pilate decided his execution, he was executed by crucifixion, and he was executed during Pilate’s governorship.[33] Josephus and Tacitus agree on four sequential points: a movement was started by Jesus, he was executed by Pontius Pilate, his movement continued after his death, and that a group of “Christians” still existed; analogous to common knowledge of founders and their followers like Plato and Platonists.[86]

Serious historians of the early Christian movement—all of them—have spent many years preparing to be experts in their field. Just to read the ancient sources requires expertise in a range of ancient languages: Greek, Hebrew, Latin, and often Aramaic, Syriac, and Coptic, not to mention the modern languages of scholarship (for example, German and French). And that is just for starters. Expertise requires years of patiently examining ancient texts and a thorough grounding in the history and culture of Greek and Roman antiquity, the religions of the ancient Mediterranean world, both pagan and Jewish, knowledge of the history of the Christian church and the development of its social life and theology, and, well, lots of other things. It is striking that virtually everyone who has spent all the years needed to attain these qualifications is convinced that Jesus of Nazareth was a real historical figure."

The idea that Jesus was a purely mythical figure has been and still is considered an untenable fringe theory in academic scholarship for more than two centuries,[note 4] but has gained popular attention in recent decades due to the growth of the internet.[8]

https://en.m.wikipedia.org/wiki/Historicity_of_Jesus

From the wiki article “Historocity of Jesus” that youve carefully ignored in other replies. Emphasis courtesy of the secular individual entitled, ‘me.’

"The criterion of multiple attestation looks at the number of early sources that mention, and evaluates the reliability of those sources. To establish the existence of a person without any assumptions, one source from one author (either a supporter or opponent) is needed; for Jesus there are at least twelve independent sources from five authors in the first century from supporters and two independent sources from two authors from non-supporters.[29][note 8] There are Christian sources on the person of Jesus (the letters of Paul and the Gospels) and there are also Jewish and Roman sources (e.g. Josephus, Suetonius, Tacitus, Pliny the Younger, and rabbinic tradition[which?]) that mention Jesus,[2][31][32][33] and there are also many apocryphal texts that are examples of the wide variety of writings from early Christianity. These additional sources are independent sources on Jesus’s existence, and corroborate details found in other surviving sources as a “bedrock of historical tradition”.[33][34] Contemporary non-Christian sources in the first and second century never deny the existence of Jesus,[35] and there is also no indication that Pagan or Jewish writers in antiquity who opposed Christianity questioned the existence of Jesus.[36][37][33] Taking into consideration that sources on other first century individuals from Galilee were also written by either supporters or enemies as well, the sources on Jesus cannot be dismissed.[29][38]

[…]

Historiographical approaches associated with the study of the poor in the past, such as microhistory, can help assess what type of sources can be reasonably expected in the historical record for individuals like Jesus. For instance, Justin Meggitt argues that since most people in antiquity left no sign of their existence, especially the poor, it is unreasonable to expect non-Christian sources to corroborate the specific existence of someone with Jesus’s socio-economic status.[52] Ehrman argues that the historical record for the first century was so lacking that no contemporary eyewitness reports for prominent individuals such as Pontius Pilate or Josephus survive.[53] Theissen and Merz observe that even if ancient sources were to be silent on any individual, they would not impact their historicity since there are numerous instances of people whose existence is never doubted and yet were not mentioned by contemporary authors. For instance, Paul is not mentioned by Josephus or non-Christian sources; John the Baptist is not mentioned by Paul, Philo, or rabbinic writings; Rabbi Hillel is not mentioned by Josephus - despite him being a Pharisee; Bar Kochba, a leader of the Jewish revolt against the Romans is not mentioned by Dio Cassius in his account of the revolt.[54] With at least 14 sources by believers and nonbelievers within a century of the crucifixion, there is much more evidence available for Jesus than for other notable people from 1st century Galilee.[55] Non-Christian sources do exist and they corroborate some details of the life of Jesus that are also found in New Testament sources.[33] Historian Michael Grant argues that when the New Testament is analyzed with the same criteria used by historians on ancient writings that contain historical material, Jesus’s existence cannot be denied anymore than secular figures whose existence is never questioned.[56

[…]

The seven Pauline epistles considered by scholarly consensus to be genuine were written in a span of a decade starting in the late 40s (i.e., approximately 20 to 30 years after the generally accepted time period of Jesus’s death) and are the earliest surviving Christian texts that include information about Jesus.[40] Although Paul the Apostle provides relatively little biographical information about Jesus[70] and states that he never knew Jesus personally, he does make it clear that he considers Jesus to have been a real person[note 13] and a Jew.[71][72][73][74][note 14] Moreover, he interacted with eyewitnesses of Jesus since he wrote about meeting and knowing James, the brother of Jesus[75][note 15][note 10] and Jesus’s apostles Peter[77][note 16] and John.[79] Additionally, there are independent sources (Mark, John, Paul, Josephus) affirming that Jesus actually had brothers.[80] Craig A. Evans and Ehrman argue that Paul’s letters are among the earliest sources that provide a direct link to people who lived with and knew Jesus since Paul was personally acquainted with Peter and John, two of Jesus’s original disciples, and James, the brother of Jesus.[46][77] Paul’s first meeting with Peter was around 36 AD.[77] Paul is the earliest surviving source to document Jesus’ death by crucifixion and his conversion occurred two years after this event.[40] Paul mentioned details in his letters such as that Jesus was a Jew, born of the line of David, and had biological brothers.[40] According to Simon Gathercole, Paul’s description of Jesus’s life on Earth, his personality, and family tend to establish that Paul regarded Jesus as a natural person, rather than an allegorical figure.[81]

[…]

Non-Christian sources used to study and establish the historicity of Jesus include the c. first century Jewish historian Josephus and Roman historian Tacitus. These sources are compared to Christian sources, such as the Pauline letters and synoptic gospels, and are usually independent of each other; that is, the Jewish sources do not draw upon the Roman sources. Similarities and differences between these sources are used in the authentication process.[82][83][84][85] From these two independent sources alone, certain facts about Jesus can be adduced: that he existed, his personal name was Jesus, he was called a messiah, he had a brother named James, he won over Jews and gentiles, Jewish leaders had unfavorable opinions of him, Pontius Pilate decided his execution, he was executed by crucifixion, and he was executed during Pilate’s governorship.[33] Josephus and Tacitus agree on four sequential points: a movement was started by Jesus, he was executed by Pontius Pilate, his movement continued after his death, and that a group of “Christians” still existed; analogous to common knowledge of founders and their followers like Plato and Platonists.[86] Jesus is referenced by Josephus twice, once in Book 18 and once in Book 20 of Antiquities of the Jews, written around AD 93 to 94. On the first reference, the general scholarly view holds that the longer passage, known as the Testimonium Flavianum, in Book 18 most likely consists of an authentic nucleus that was subjected to later Christian interpolation or forgery.[87][88] On the second reference, Josephus scholar Louis H. Feldman states that “few have doubted the genuineness” of the reference found in Antiquities 20, 9, 1 to “the brother of Jesus, who was called Christ, whose name was James”.[89][90][91][92] Tacitus, in his Annals (written c. AD 115), book 15, chapter 44,[93] describes Nero’s scapegoating of the Christians following the Fire of Rome. He writes that the founder of the sect was named Christus (the Christian title for Jesus); that he was executed under Pontius Pilate; and that the movement, initially checked, broke out again in Judea and even in Rome itself.[94] The scholarly consensus is that Tacitus’ reference to the execution of Jesus by Pilate is both authentic and of historical value as an independent Roman source.[95][96][97]