I've been thinking about how you describe Critical mode to have less HP, making the fights shorter and faster, and I've had a bit of trouble figuring out how to describe the following, but here goes.
It is not that enemies
have less HP on Crit compared to other difficulties, if you compare their full HP you can see that they have the same amount, it is the fact that Crit is balanced in a way that makes Sora deal more damage than on Normal and Proud.
Not sure about Beginner, I think Sora might deal the same damage in Beginner, but since Crit gives you an extra Finisher you still deal more damage per full Combo.
The higher damage output just gives the illusion that enemies have less HP even though they don't.
I can't really find any videos that talk about Sora's damage output differences in the various difficulties, only videos showcasing defense comparisons.
https://www.youtube.com/watch?v=j20lfY-D2jU
https://www.youtube.com/watch?v=-IqJGJ70R4E
The closest I could find is Bl00dyBizkitz's explanation of KHII's damage scaling system.
[video=youtube;Q9v1fjXKZUs]https://www.youtube.com/watch?v=Q9v1fjXKZUs[/video]
You can tell he was asked a question during a stream about Sora's damage output which he was not prepared for, but it is still interesting to see how much effort was put into this game's gameplay mechanics when the story was not given nearly as much attention.
*Damage scaling (to make sure you're never trulyunderpowered nor overpowered)
*Revenge value (to make enemies retaliate after being comboed)
*Flinch counter (to make sure enemies can't be endlessly comboed, different from Revenge value but associated)
*Magic, Drives, Limits and Summons connected to Physical Combat (to make combos more fluent, when in KHI Sora would stop in his tracks to cast a spell)
*Keyblade Abilities (to make most Keyblades still useful for something late-game)
All things that make a lvl 1 playthrough possible without giving 'EXP Zero' hidden properties that ensures enemies can't one-shot you like in 1.5.
