She's not an "it"!
Well since almost everyone involved with the series voice acted at least once before - either for the KH series already (original character voice actors) or Disney voice actors (in the blockbuster films), I think it's safe to say that it's the direction. Riku is the most painful one to watch in KH3 because he is like a brick wall, probably horrible direction to have Riku seem "stoic and mature". It's also hard to voice act when the animation is just characters looking at each other and not really doing anything else besides talking and/or just being exposition, which is basically reading lines of information (see Ienzo).Sora's voice acting is perfectly competent and often quite brilliant. It is very very rarely subpar. He gets the tone, inflection and delivery right most of the time, unlike many of his co-stars.
I don't care how well-known actors are. Nor did I claim well-known actors would somehow sell more copies. I care about competence and quality. Many times, that correlates with star power, but not always. Not mostly, either. I don't care to find out who the Disney actors are because they're either good or simply unobtrusive. No one is expecting oscar-winning performances, just ones that don't take you out of story. Many times, perfectly good film actors do terrible jobs on KH because it's either not their medium, they had crap material to work with, or they were directed terribly. Mostly, though, I fear the biggest issue is actors aren't really acting but reading lines off a page without any context. It's quite literally phoning it in. Compare it with the astonishing performances in The Last of Us (which uses motion capture with actors on set).
I'm honestly surprised how many are content with acting quality among KH fans. I don't really watch dubbed animation, I'm more of a cinema freak, so could it be I'm just unaccustomed to it? I'm happy to concede the issue lies with me, just want to understand it 'tis all.
On topic, I wouldn't mind a Yozora game, though I'd only play it because it's connected to KH. Otherwise, the genre really isn't for me. Ten years ago, I'd have been smitten for the Yozora/Verum Rex stuff, but it seems like I feel ive grown out of that grown up stuff now.
But circling back to your issue, what was wrong with Yozora's voice acting? I thought Dylan Sprouse did a pretty good job.