358/2 is the only one I can kind of enjoy, the others are just a slog and a half to play through. BBS and DDD control like garbage and the command deck is a flawed system at it's core, and CoM is an interesting idea with bad execution. Can't really speak for Coded or X, but from what I've seen of them they're not my cup of tea either.
Also you're right on the point of the accessibility no longer being an issue, but they're all still guilty in adding more plot holes and elements to an already confusing mess of a series.
The series isn't confusing though. Convoluted and a bit bloated, maybe, but it isn't confusing. When you actually sit down, play the games, and follow along, 95% of it makes perfect sense. The remaining 5% is just residue left from the retcons and crap (which I'm not defending, to be clear).
It's no more confusing than following the Harry Potter books/movies or following the MCU, or following something like Naruto. They're just really long, bloated stories that span over a decade (or will soon) of installments. It's for this reason I always describe Naruto as "the Harry Potter of anime" and Kingdom Hearts "the Harry Potter of video games" when explaining it to casual gamers and general pop culture enthusiasts. All three are franchises with many installments that tell this really long story over the course of around a decade, and feature a magical boy protagonist that we follow from boy to adulthood. It's also for that reason that they are best appreciated by people who started watching the originals when they were kids themselves because it's like a friend you grow up with, and of course the cast of characters the protagonist is connected to grows larger with each installment.
Kingdom Hearts 3 is going to be confusing to anyone who hasn't played the previous games because yeah, it is carrying the baggage of like, ten games. Even beyond lore stuff, I guarantee you there will be tons of moments meant to tickle the heart strings of fans, like, as a random hypothetical example, playing through a flashback of a classic event in the KH3 game engine. Something that won't require knowledge of the lore to understand, but something that requires the years upon years of emotional investment in these characters and worlds to truly get the emotional impact from. Same for if, again hypothetical, Sora and Kairi were to officially become a couple or kiss or something - there's nothing complicated in relation to the lore there to understand, but their relationship was built up to in previous games so that payoff doesn't mean anything if you haven't had the years of experience playing the games to get attached to the characters.
Which is honestly my bigger concern for people who haven't played other KH games yet insist on jumping into KH3 because it's popular. You don't need to fully understand the lore to get into Kingdom Hearts, or Harry Potter, or Naruto, but if you haven't experienced the previous installments, then the emotional payoff of the finale of each series means nothing to you, and that's a bigger shame than not 100% understanding the lore.
Honestly, the deep lore is only there for superfans really, similar to the superbosses and other extra content in KH games.
Also I disagree with the Command Deck being fundamentally flawed, as Re:Coded implemented it flawlessly.