Everyone thinks stealth characters are weak but they don't always need to be light in hp and have armor. Get the deep green perks and you're set. Fighters can get knocked around in a fight but stealth sneaks up and slits his throat he can't do crap. Whats a sword gonna do when yer dead.
For one thing, with stealth characters you are good at a lot more diverse stuff than fighters. You can pickpocket(which isn't that useful but its fun), you can pick those annoying expert locks, you can bribe people, plus you do a lot of damage with sneak attacks. And stealth perks are better than fighter perks.