Good day! I am trying to find a good alternative as not to use the"smart" functions or using an Xbox to consume our media. I found a few options ie like plasma big screen but it’s no longer in development. Essentially I would line love to have it running on an rpi4 and just hooked up to the TV.
You answered your own question. As you said, most smart TVs go into a sleep mode, so they appear to turn on in a near instant. But if you ever actually power it down, most take up to a minute to boot up.
Dumb TV’s are the same they go to sleep. You need power for the remote to work.
I just got an LG C3 and don’t have it connected to the network. I also turned off the fast input and power on and takes maybe 10 seconds to boot into the input. Not much longer than my blu ray player and receiver.