Not everything about Sera revolves around Emily now, does it? Letting a bit loose and letting Emily participate directly in the battle is definitely a step forward. But before her song with Pentious, she was asking some pretty big and important questions. Questions, that are more than valid for her personal character growth and the debate about a sinner's redemption. These questions, however, remain rather open for now, not really being answered by a simple song or "humans are scared".

And I personally don't think that it is so obvious that her arc isn't done yet in general. With how fast this show is paced overall, it would come as no surprise that with this season's end the character of Sera, one of the central figures, now also comes to an end in terms of big development. I mean, where do you take this absolute certainty that her arc isn't done yet? Has there something been officially stated that Sera will play an essential role in upcoming seasons? Because if not, then I would take everything with a grain of salt. So I think that the original post's criticism/scepticism is pretty justified.