I second that ice grenade is far better than other.
Some ways to improve other skills:
- Greatly reduce enemy's damage output for longer periods, like, after concussion enemy has some 50% chance to miss completely for, say, two turns, and overall damage decrease by 25% for three to four turns (overlapping with miss chance), so, basically, you can keep SINGLE enemy mostly locked out of combat indefinitely.
- Some kind of friendly fire from fire grenade, like burning enemies additionally damage each other (will be useful against larger groups), maybe chance to miss, too, or even attack each other instead of MC.
- Bloodlust can be adjusted or reworked by adding EXTRA very random attack. Either 50% chance to shoot enemy for half damage (improved), or just no damage increase and extra attack against random enemy for some percent of damage, likely half or 67%.
- Nanites can grant very temporary immunity (or very high resistance) to corruption gain OR to statuses from enemy's special attacks like corrosion or fire or whatever.
The biggest problem, of course, is balancing. These are just ideas of something that will make me personally consider using other skills, and even then these numbers are extremely preliminary.