I don't put a lot of stock in the listed weights either and nor do I actually put a lot of stock in what guys currently weigh. Strength and conditioning and modern sports science are great but imo (and maybe I'm old fashioned in thinking this) there's a difference between a Big Guy, and an average sized guy who has lifted a lot of weights.
Vaimauga for example has clearly bulked up and none of us know what he really weighs right now, but he's only about 6' tall and he certainly isn't built like a Junior Paulo or an AFB. He's a pumped up backrower.
Likewise, Bunty at some point ate/pumped himself up to 110kg+ but he's just not a truly big guy like that.
Anyway, we have what we have and it's true that a lot of top forwards in the comp these days are around that sort of 6', 100kg mark. It's probably more that there are particular situations or match ups over recent years where we have been a bit helpless to stop bigger and more athletic opponents, but I'm probably focusing too much on specific scenarios.
Actually the "naturally" biggest guy we have at the moment is for sure Niukore