Stealth in OB is about a lot more than plinking arrows from a dark corner, or backstabbing. It can also be about messing with enemies' minds and making them fight each other with Command/Frenzy spells, or other types of misdirection, like Conjuration. I really do enjoy sneaking into a dungeon full of NPC enemies and beguiling them into killing each other while I watch from afar, only needing to kill the last one standing with any form of direct damage. Or perhaps a Summon combined with an Invisibility effect.
I don't level cap my characters as a general rule. Sometimes. But, once it becomes impossible to one-shot a Bandit with a sneaky arrow alone, there's still Poison, Destruction, Illusion and Conjuration. Destruction doesn't get any bonuses from concealment, but it's still very possible to sneak-kill an opponent with it. Sneak up behind them, and use a Touch spell that contains Paralyze and Weaknesses in order to capitalize upon effect stacking. Using your Block button/key, it's also possible to fire off a spell once every second instead of every two seconds. You can utilize this mechanic in order to fire off a barrage of a spell at an unaware target, oftentimes killing it before its AI tells it to move out of the way.
In case you hadn't noticed, I enjoy the stealthy use of spellcraft... quite a lot.