Except BB was still critically acclaimed whereas GL couldn't be further from that. Your missing the point.
Sure a potential (unlikely) sequel for GL could be better but there has never been a SH origin movie where it's been critically panned and then suddenly its sequel is incredibly amazing? Yeah sorry, but that's not going to happen.
The best turnout that could happen would be a FF to Rise of the Silver Surfer deal and I doubt thats what most GL fans, SH fans, and the GA want at all.
I don't consider that a success story at all. Why keep building on mediocrity?
The comparison is inherently flawed due to the fact that BB is still a far better movie. You can bring up the subjectivity point all you want but BB is plain and simple a much better structured, acted, and thought out film.