Y'know, Jafar's guardsmen fighting with stolen keyblades would actually make for an interesting boss fight.

Well that's a prequel story, but still I get what you mean.

Basically the main reason why Sora's keyblade was really notable at first was because he was one of the first new keyblade wielders in over a decade, and as shown throughout the series he's also one of the few who is basically a real cinnamon roll who can't be easily corrupted unlike some of the keyblade wielders of the past.

In fact… IIRC wasn't Mickey the last "new" keyblade wielder before Sora? I know he was the last person to become a master in the time between Birth By Sleep and KH1, but yeah as I said I'm pretty sure that in the decade between BBS and KH1 there were no new keyblade wielders until Sora (and then Riku).

(Also I don't really play Union, all I know about it is like one part of the story is pre-Keyblade War and another part is post-War and it's arguably "harder to follow" than the main canon due to some confusion over how some stuff fits into the timeline, but I don't expect KH3 will really bother acknowledging stuff from Union, just the past console and handheld games that you can now conveniently all play on PS4)