To be perfectly honest, I dont really know what they can do. They are fine as skill trees and are obviously better made for pve based activities. But if I were to make any suggestions... Top tree striker could regenerate some melee energy on grenade kills. Bottom tree sunbreaker could apply like a debuff that applies when you damage an enemy with a grenade where if you kill them within 2 seconds you generate a sun spot. Not like a normal debuff, basically like an effect that does nothing to the enemy, but lets the titan activate it. As for sentinel...I don't really know. Its neutral game is so scattered but it's mostly tailored for pve. Sunbreaker...the same thing kind of. It has bonuses for the super and it's fine that way. Most of my problems with these skill trees could probably be worked around if grenades in general were more lethal. Killing with grenades other than stickies and pulse on titans is so infrequent so you basically only have the melee to work with.