It's a lot of work to implement solid combat stealth. I've played Baldur's Gate a lot, and have messed with the codes too, so I have an idea what it's like if you want AI to use and counter stealth in a reasonably smart manner.
So I suppose we could just start with the popular "2 AP sneak". By default, you need Sneaking rank 5 to completely negate movement speed penalty, and I think that's alright. Then Guerilla deals 250% damage? These could certainly be starting changes - not too radical, and sounds reasonable to me.
Yeah, those changes seem to make sense to me. I suggested boosting Guerrilla to 210-215% base damage as the bare minimum to make it useful, but taking it up to 250% would probably be fine.
On the other hand, I'm also okay with Guerrilla being changed to explicitly only work for the first attack from outside of sneak, but it would still need a substantial damage boost to make it worth spending one of 5 Talent points for something which is so restricted in its use AND requires a lot of planning (and usually, reloading) to use properly.
However, I don't really think "it's not realistic to sneak when standing behind someone" is a great argument in this game where every third person on the street has super-powered "do anything magic". The realism ship sailed out and sank long ago. Gameplay balance is more important than strict realism.
