Well firstly, if you're average or lesser irl, you'll want to be awesome in a game, and if you're awesome irl, why would you want to play a lesser person ? Secondly, to do what you usually do in games like this, the PC has to be exceptionally skilled and powerful. If Hawke hadn't been a world-class badass s/he'd have died to the darkspawn in the prologue, or even at Ostagar in the case of warrior or rogue Hawkes.
Personally I like being OP because I play for immersion and don't care for challenge. I want my character to be as powerful as possible so I can mow down everything. How is this fun you ask ? Why do you find struggling against mooks fun I reply. Also, for immersion. Someone who can fight and kill high dragons or defeat whatever uber thing the final boss is having trouble with a few human soldiers makes no sense. For exemple, mage Hawke defeated Corypheus in a magic duel, this makes mage Hawke one of the most powerful mages in history, fighting regular enemies should be akin to frying ants with a magnifier for someone like that (which it is when you play on easy with a "broken" build)