Regarding to Nihilus' mask, why can't you actually *wear* the damn thing? Sure, you pick it up and carry it around as it supposidly increases your powers, but both games have lacked good masks to actually wear.
I think one of the reasons Nihilus is so pathetic is because, since there's no level cap, it's much easier to destroy him by that time in the game. But still, he should have been much tougher as yes, he would have been one of the tightest Villians in history of SW.