Personally think that most of the human bosses are disappointing.
Davy Jones and Xehanort are exceptional.
Anti-Aqua is just zodiac Aqua, so if course she's good
Dark Inferno is cool, but lacking for a super boss.
All of the rest of ORG 13 just lack the pizzazz they should have.
The best of them was Larxene and Marluxia due to their desperation attack tag team and The Xehanorts cause of the keyblade spam.
But otherwise they just didn't have the oomph. Like the titans are garbage, but everything you do against them is way cooler than what you do against the ORG members
Those fights needed to be one of two things.
They either needed to be more complex. Like Aqua. She's got like 15 unique attacks to each org members... 2 to 3
Or they needed to have more cool things being done like all the giant bosses.
It's really kind of wild how well executed the Davy Jones boss fight is. It's definitely one of the few examples of the series' balancing sensible boss design and pitch perfect aesthetics.
As far as the Org XIII bosses go, I think the movesets themselves are mostly fine (with Marluxia, Larxene and the Xehanorts being the highlights, as you already noted), but there's a few things working against some of them:
- Xigbar in particular isn't as engaging a boss as he was in the past for one main reason: You don't really have to work to even catch him. In KH2 and even BBS, part of the catch with his boss battles was even getting a hold of him, be it through teleporting constantly like in BBS, or a combination of that and changing the arena terrain like he does in KH2. With the boss arena you're given here, you can camp out most of his attacks (Though his desperation move is really cool), and his teleporting is more or less rendered ineffectual thanks to airstepping, and you get a free combo out of that to boot! I think a somewhat smaller arena and more aggressive AI would do that fight wonders.
- Dark Riku is interesting because aside from the two new moves he has (the floating mines he'll surround himself with and that shadow claw attack he tends to follow that up with), he's more or less a cut down version of KH1 Possessed Riku. Blocking and countering the blade he throws still blows him up as easily as it did in KH1, and his desperation move isn't particularly difficult to get around at all. I think he definitely needs a few new moves (He doesn't even use Dark Aura!) and needs to be far more aggressive.
- Terranort is a joke as is and absolutely needs more attacks. He only has three, and he spends most of the time doing that dumb dashing attack (Dark Haze?) over and over. HIs desperation attack is okay, though.
- I actually don't have to much of an issue with Vanitas as is.
- I don't even know what the finer mechanics of Saix's berserk meter are supposed to entail because Roxas kills this guy on sight.
I think as far as the game overall is concerned, Anti-Aqua is far and away the best humanoid (Or hnestly, probably the best overall) boss in the game, with the triple Xehanorts in a distant second.
