I think comparing that era and this era is a mistake, besides if Lemmy lets say goes closed source which is EXTREMELY unlikely to happen, someone will not make the mistake again to not fork it to keep an open source version going.

besides it’s not just open source, it is also the FEDIVERSE, this is the most important, this platform is federated and decentralized unlike Reddit ever was as it has always been centralized by design. Both Lemmy and Reddit are very different from design here.