Been evil also doesn't mean you HAVE to make only evil choices.
So no, "evil playthrough" by no means force you pick only evil options. And there are plenty neutral options to pick.
Generally, I agree with your first point. Much of the time a polite evil character would do something similar to a good character but with a different motivation. The flaw in the game is that there is rarely payoff for that alternate motivation.
I think a good example of how to make this work is choosing to kiss a foot in order to submit or to steal a ring.
