You’re not abusing sleights enough. If you set aside maybe 30 minutes to build a sleight deck for your level the game becomes an utter joke.
The only cards you should actively be using are 0 cards (to break supers) and items.
See, people joke about KH2 being “press triangle to win.” That’s secretly COM’s deal.
Make “cascading” sleights, since using a sleight will use up the first card used in the sleight. For instance, Blitz will work on any three attack cards whose numbers add up to be between 10 and 15. The “ideal” deck for this is all 5’s, but since you probably don’t have that, structure your deck so you can just mash triangle, when you run out of attack cards reload, proceed to mash triangle again. E.G. For Blitz a truncated example might be 5 5 3 5 2 4 6 2 -> 5 3 2 4 6 2 -> 3 2 6 2 -> 2 6 2
Early game (after level 17) build your deck around Blitz, then later Sonic Blade (or tornado, but Sonic Blade is better for certain bosses), and finally Ars Arcana. Throw in a couple potions for recovery and 0’s for breaking boss attacks and laugh as bosses and enemies melt.
Also, when you level up, never take health. You don’t need it if you abuse sleights.