this whole "a dominant champ makes a division look weak" thing is one of the biggest myths in MMA.
GSP, while not a finisher, has made every opponent he has faced look just plain bad, like they didn't belong in there with him. He was just a step ahead of his opposition, yet WW is routinely listed as stacked. GSP's dominance (and yes he is, as you would say "fuckin dominant") hasn't made the division look weak whatsoever. Hell, WW has had nothing BUT dominant champs throughout its history, yet it's still stacked.
Aldo at FW is another example, he's easily one of the best fighters on the planet (I have him #2 p4p), yet FW is routinely listed as among the most stacked.
most of the best LHW's started exiting their primes (or were already past their primes) when JBJ became champ, and there isn't a sufficient crop of talents to keep the division stacked.
MW has been a. divided between the promotions (more so than any division above 145 except for LW IMO) and b. has legitimately been weak (although nowhere near as weak as the haters like to make it out to be) in it's past. It's building up now, that's good, but that doesn't make it a historically stacked division.