Fixing both Leech and Combat kid would be as simple as making Leech heal only when you deal damage, maybe you heal X% of your damage you deal with autoattacks. This increases your longevity without heals, but you can't just soak up your own blood to heal for more than you're taking in damage. It also means you'd only get heals on your turn, so comeback kid wouldn't be able to keep you alive through several attacks.
As for sneak I'll quote myself from
another thread -
Currently, it's optimal to get Sneak 5 on every character if you want the easiest combat experiences.
It's boring and cheesy though.
Now, I'm going to preemptively bring up the "Single player game don't use it you don't want" argument.
This does not apply here because you can't use sneak without it being cheesy. It should be a fun and balanced element of the combat, but due to AI not being able to handle it, you can't really play a stealth character in an enjoyable manner. It ruins stealth characters because it's so broken.
What would be nice is if stealth offered real in-combat benefits but was not a near 100% reliable way to cheese every fight. This means changes like giving the AI a sort of "memory" of where stealth characters were when they last saw them. They should be dropping AoEs, or melee should move towards the spot to regain vision on them.
There might be other needed changes but at the very least AI needs to sensibly react to the tactic of stealthing at the end of every turn.
