Sure, but why have the First Evil simply vanish? They build up this big battle all season long, with all these hints about the FE becoming corporeal, making it obvious that at some point the creators were planning a showdown between it and Buffy. It's one thing to do away with that, it's another to scrap the idea of a conclusion altogether. Not having any sort of confrontation between the hero and the bad guy at the end of a story arc explicitly building up to that confrontation isn't dramatically fulfilling. It's just bad writing. I don't know how you can defend that alone, and I won't even get into all the abandoned FE plot points, like the meaning of the "From beneath you it devours" line, the weakness of the Slayer line that was never explained, what the whole deal was with the appearance of Joyce to Dawn (was it the FE? if so, what was the meaning behind that "Buffy won't be there for you" line? it meant so much at the time, brought up so many questions, yet was never referred to again), how Giles survived that axe to the head, etc., etc...