Its ironic that the very reason WW was hyped as a strong division for so long is actually why is was a relatively weak division so long. That is the UFC being the only org to seriously invest in it during the early 00's, unlike 155, 185, 205 and HW they did have most of the best talent and as a result hyped the division a lot. That also ment however that the overall investment in WW was very limited AND focused mostly on US wrestlers.
The way BJ moved up to 170lbs dispite actually being capable of fighting at 145lbs without dropping much muscle and beat the #1 fighter shows you just how weak things were. Equally Fitch was able to be the #2 fighter for years on end dispite relatively few big wins and with quite a limited skill set, good but not awesome wrestler, passable striker and sub fighter at best. You compare that to say Nog at HW who was an elite sub fighter and an excellent striker.
You also look at whats happened more recently, guys like Lawler, Maia and Palhares have moved down to 170lbs and cut though much of the division. The reason being IMHO that WW at recently as 3-4 years ago(and so some degree still today) was weak in terms of striking and submission talent being heavily wrestling focused.
For all the talk about Pride HW legends being "out evolved" I actually think that its WW and MW that have evolved a lot more since most of the reign of the UFC's hyped GOATs in GSP and Anderson dispite those reigns being latter than Fedor/Nog. HW back the early/mid 00's had elite striking, submission and wrestling talent involved with a lot of well rounded fighters at the top, WW was mostly wrestlers and MW mostly rather one dimensional fighters even into the late 00's.
The explanation is simple as well, HW had serious investment in it way way before 170lbs and 185lbs going back to the mid 90's, MW and WW really only had serious investment in them as GSP and Andersons fame took off which took a few more years to feed into more talented divisions we have today.