Definitely not. And going back through the games, the way a lot of them were used was kinda awkward and weird.
Like with Aerith and Yuffie and Leon in KH1, they were basically loredump machines, explaining stuff about the Keyboard and Heartless and the like to Sora that literally anyone could have done, but there weren't many options at the time, and so the FF cast was used.
KH2, similar deal, except this time Leon and CID and Aerith and all them were basically used to set up the foundation for Tron's world and also some stuff with the DTD/setting the stage for the Ansem the Wise reveal, which, again, anyone could have done (which is made most obvious by having Mickey be the one to actually finish off that plot thread and actually explain most of that stuff in the end, even after the hard work of characters like Leon to get access to that days).
But now, not only are there characters like Mickey and Yen Sid and Ansem the Wise himself wandering around, bit you also have characters like Ienzo and Even and the like, who can very easily fill the ropes the FF cast used to have at explaining random things about the lore. They were only used to do that in the first place because of a lack of options and having them available.
But now that options are hardly lacking anymore it would be kinda weird for Sora to double back and ask, say, Leon, about the Keyboard and what to do next instead of someone like say Mickey or Yen Sid or Aqua/Terra/Ben or Ansem the Wise or one of his apprentices like Ienzo, etc. He has so many good resources for help that some random cast of characters that barely have any reason to know much of anything about this stuff are kinda low on the list.
And then on a lower tier below characters like Leon, you have the characters who truly were just cameos through and through, like Tidus and Wakka and Selphie, who, even back when I was playing KH1 as a kid for the first time honestly just kinda bugged me due to how obviously out of place and forced in they were. They were just kinda, well, there on the Islands. But Sora, Riku, and Kairi barely ever acknowledged that they actually existed and treated them as if they might as well have never been there in the first place, so, well, considering that's how the MCs of the game itself treated them, it's no surprise really that I myself adopted a similar attitude toward that type of character and can't say I really miss them personally considering they were barely treated as though they were actually ever even there to begin with.