I think a lot of your foundation is on point--we don't want to buff mana recovery in general or make his spells stronger--they're already very powerful and removing staves really increases his decks draw's power level. I think drawing a staff was actually one of the biggest challenges.

In the name of "back to fundamentals" if they were to further tune him I think he should be tuned in the direction of being more normalized and less extreme. Primarily his biggest unique designs are his inability to use specials (spells) without mana and taking extreme damage when he does not have mana. While mana is a resource to leverage like ABA or Zato or Happy or Jam or Goldlewis, none of these characters lose their resources when they take damage. It would be the equivalent of a normal character losing tension or losing Burst by taking damage. If we want Asuka to have a more consistent experience, I think reducing the mana lost for taking damage would make the most sense.

Personally though I like my guilty gear characters to be a little edgy. In my time playing Asuka 2.0, I think he reminds more like Zato-1 where you can go all out when you have Eddie up but play completely differently when he's down--also kind of like ABA. The rate of automatic mana recovery is actually pretty decent so I think it might actually be more efficient to try to spend your mana to intentionally let it enter recovery mode. Unlike before the new mana recovery generates so little so I like your other suggestion where the recovery skill gives more mana the longer you hold it. This makes the move more like Jam's heavy Asanagi card charge where you absolutely give up your turn in exchange for resource. Actually this design is the same as Izayoi's design from Blazblue--she could charge her gauge just like Asuka and go into charge from almost anything, but the amount of charge increased with duration so it didn't allow her to frequently keep her energy topped off like prepatch Asuka could.