How is DDD confusing? I have never understood that, as for the other games in the series, I'd recommend playing in chronological order, it's simpler that way.
The problem is DDD retcon's Ansem SoD's cloak form. Introduces time-travel, and virtually starts to allude to "if you played the phone games, what we're explaining in DDD should make perfect sense."
You can make a game as accessible, you can make it free, I'm not gonna play it, I will sooner watch someone else play the mobile game or wait for a summary than participate and call my personal stubbornness on the matter what it is (keep it stack) I have no desire to play the phone games, just how it is playboy.
Birth By Sleep having to needlessly explain that ceremony to pass the power of the keyblade to a successor, which is only ever done once in the entire franchise...? Just to supply Riku with context in the first game for why he was originally destined to take the kingdom key in contrast to Sora. We later see a back and forth in the first game on "what constitutes" you being worthy as Riku takes it back from Sora, and then vice-versa, that whole tug of war thing wasn't explained very well, and it borderline make BBS attempt to explain passing the power somewhat like it fell on deaf ears. No one's listening, no one cares, because it's quickly pushed to the back of the room and made irrelevant by other unpolished ideas and concepts that just take priority over that argument that's been made for decades now.
If the OP is talking about the games as standalones, multiple playthroughs would resolve issues to some degree. Its very similar to having watched a film multiple times to spot the easter eggs or pop-culture references. If we're talking about a time-line, transitioning across multiple games in an entire franchise, complaints about the story (even in a vacuum) it's still difficult to follow.
If you want my honest take on the timeline, kingdom hearts basically starts to feel like that shoenen Naruto, Kishimoto had all these ideas for all these characters and couldn't properly excecute all these individuals stories and make all of these characters relevant for their own personal arcs, all at once. In the case of kingdom hearts, look at it with reading glasses or basically the hunger games (the books, not films) and tell me does it do what those stories do? A franchise that builds 60% of it's identity on marketing Disney IPs, world travel, telling half-paced stories of fan favorite films, and the troupes are what get baked into the main character who they (game after game) rob of any real development up til DDD where he's made painfully aware that people that are suffering are "locked within himself and need to be freed/woken up".
Let me know if any of that was hard to follow, because explaining that to someone thats only played every single game a single time, they'll barely understand what the heck your saying and rightly so. A more fair playing field, would basically require you to play the games multiple times over, read the in-game journals and bestiaries, secret reports, etc since the game can't just tell you EVERYTHING through it's own merit in terms of its narrative.