I don't really care what alignment the romance companions are for me personally. I'll romance whoever appeals to my taste. The OP doesn't feel that straight male players have good options in terms of "good aligned" female companions. Perhaps he doesn't find those female choices attractive.
I can't speak for the OP, but from the initial post, that was not the issue he was concerned about. It is that none of the female love interests are non-evil. I think he is possibly wrong though, since I suspect Karlach might not be evil. (It is difficult to tell since 5e stupidly removed alignments.)
So yeah, Shadowheart, while often annoying, is almost certainly a good person at heart.
Even if that were true, and I don't think it is, it doesn't help since she will be perceived as evil when players are choosing a romance option.