I actually have the show on right now ... if anything I'm seeing how well written it is.
Yeah, you don't know.
Okay, so here is how it is: suspension of disbelief has nothing to do with how in-character you think a character is. It's about simply the act of accepting you are watching a fictionalized performance of narration. Every piece of fiction, no matter how 'realistic', like the Wire, never happened and thus, when you sit down and watch it, you are accepting that you are going to pretend that Daniel LaRusso is a real person whose truly interacting with the world he's in. That's suspension of disbelief.
As for what you just wrote, to be honest, I don't really care because I find this whole Daniel LaRusso thing to be a farce, but to throw you a bone and take you seriously, I wouldn't say that anything you're talking about has anything to do with believability.
You keep talking about these 'nods' to the movie the series makes. That makes things
less believable, not more, because the vast majority of people end up in careers that have fuck all to do with what they wanted as kids or were doing as kids. If they wanted to be believable about Danny's job, he would be doing something totally unrelated to what he did as a kid. He'd be a chef or financial analyst or a vetrinarian or a travel guide, whatever. Or, btw, there is a significant amount of people that were doing good as kids and yes, their life has fallen apart and now struggle with alcoholism or whatever, so THAT is realistic too, for that matter.
So, what you are talking about, with these nods? It has fuck all to do with believability.
What you want, and what you are describing, is deriving satisfaction from KK series from providing, it's is nostalgia. "Oh my god, Danny is a car sales man, which is connected to the first movie, that
I saw when I was a kid! How beautiful!" It's narratively satisfying because that's what you know of Danny's life, his relationship with Miyagi, pays off in Danny's later life, etc. It's the same reason why you have tons of kids/YA stories where the love interest end up together and stay together, even though the vast, vast majority of people that end up married tend to marry someone they never knew in school. But that's not narratively satisfying to the audience of that genre, because it feels random to say "And then Harry Potter married Christine Smaultz, who he met 8 years after the end of the series" as the epilogue because that feels random. Which it is, because life is random. It doesn't do "nods" to the past.
And there's nothing wrong with narrative satisfaction, but it's far from realistic, so stop telling me how much believability to you didn't have to suspend, because you very much did.
Anyway, Luke's character arc in TLJ was one of the best thing SW ever did.