I know what you said, and I'm disagreeing with you. The only Disney worlds that are mostly main plot relevant in KH1 are Monstro, Agrabah, and Neverland. Yeah Atlantica gives us a good bit of background regarding the role of a keyblade wielder through the Triton scene, but its connection to the main plot is pretty weak overall. You can outright skip it, in fact, as I recall, with no change to the overarching story.
Meanwhile Deep Jungle isn't connected basically at all, Olympus and Halloween Town only have villains we know from other scenes are in league with Maleficent (despite the plots of their worlds having seemingly nothing to do with The Plan), and Wonderland had Alice kidnapped for the plot offscreen. And that last one, if you visit Deep Jungle first the scene with Alice has Snow White in it instead and you don't discover Alice's fate until Hollow Bastion.
Even if we go ahead and count Atlantica because of Ursula's connection to Maleficent and the whole Sora-Triton exchange, that's still just 4 Disney worlds out of 8. Or 9, counting 100 Acre Wood which is also not plot relevant.
Now, that being said, I do feel like KH1 did a good job of creating semi-original stories, where KH2 preferred to shot-for-shot retread world stories. But in my eyes, both main titles had more main plot irrelevant worlds than relevant ones, and I'm personally excited that KH3 seems to be making every world relevant (except possibly 100 Acre Wood?).