I don't think it's fair to blame Sera Gamble for everything that's ever been wrong with SPN - the writing was horrible before she ever came along.

The quality of the plot was never the reason why I watched the show; at it's best, the show had some charm because of its unintentional cheesiness, but mostly because, by some good fortune, it happened on a very interesting character dynamic with the Winchester family (including Dad), and had one (and sometimes two) actors who were able to lift a mediocre script into excellent characterization moments. But whenever anyone attempted ambitious plot... major ouch and headdesk time.