The thing about rogues is that if they are sneaking properly, they will *never* get hit.
Ok, fair enough. How is this different from a 2h Warrior w/ Sneak? Except for the fact that he deals double damage w/ sneak even without Guerilla and also has the ability to sneak in to the middle of a group and wipe out the entire group in 2 AOE hits?
The only advantage said Rogue has is more movement speed, which doesn't really matter because the Warrior can do his strikes from the side while the Rogue needs it to get behind.
I would argue that a warrior who is sneaking is not much different from a Rogue, but you're right; 2H will deal more damage than Daggers when taking skills into account. This stems from the fact that Daggers are 1H weapons (and are Dex based) compared to the Str-based 2H weapons of the Warrior.
Backstabs do get an increased chance to hit though compared to attacking from the side, which will lead to the enemy turning around less often.
That, and attacking with Daggers uses less AP, which means that they can be more versatile with their attacks; it's much easier for a Rogue to hit-move-sneak than it is for a Warrior thanks to the AP cost difference. This in turn makes it easier for the Rogue to be in a good position in Sneak mode at end of turn so that the enemies don't attack.
Actually, does Guerilla even work with Skills? From what I have seen it doesn't, since the characters exit sneak mode just prior to casting the skill (it says Sneak Failed), but my eyes could just be playing tricks on me.