Sera being a waste of space in my roster that I literally never want to use again is a success? That's a valuable roster spot that could be filled with a character that actually deserves to be there.
This is the exact same way I feel about Alistair. He literally spent all his time in the Party Camp playing with his dolls until his plot armor forced him on me. So, who could I replace him with again? Oh yeah, Loghain, at the end of the game, and guess what, I did it every time. The moral to the story? Just because I don't like a character doesn't mean they are a waste of space, considering how much "squee" Alistair gets, eh?
But let's take this comparison a bit farther, shall we?
Petty: Reading this thread, it's apparent that people see Sera this way. Can we point out any instances of Alistair being petty? The short answer is yes, and a good example of that is selecting the surprised answer to "I'm Maric's son". "I can't marry you because you're not human". Hmm, seems like one of the "popular" characters in the lore shares a lot in common with Sera, only, it seems, he gets a pass because reasons.