first off gsp tried tremendously hard and with strategic planning to put on the weight to fight at mw. It didn't go well at all for him, his body rejected the attempt causing his colitis issues, sure he was bloated but at like 60% cardio, at ww gsp never gassed, even after a 5 round dominating win he still had gas in the tank, so mw was never for gsp and fighting there killed his gas tank which he was well known to have as a ww.
Gastelum is just another fighter that should have never been fighting at ww, he always should've been a mw like many others doing or have done the same thing, in gsp's defense he is a natural ww its the division that fits is physical make up perfectly in this sport, not for gastelum.
als gastelum has problems making weight, multiple times as a ww, and for the bisping fight he was over.
https://www.bloodyelbow.com/2017/11...telum-needs-two-tries-to-make-weight-mma-news
"Your other bit of weigh-in drama came courtesy of Kelvin Gastelum. While Michael Bisping had no problem making weight, Gastelum was the last to step onto the scale, and for good reason. Gastelum initially weighed 187 pounds, but on the second attempt, towel across his body, he got down to 186. This is yet another problem for Gastelum at the weigh-ins, having missed multiple times at welterweight."
I also give gsp some credit for gastelum's win, that fight came way too early after the gsp fight, and even though bisping was cleared to fight gastelum those shots he took from gsp and the choke I'm sure didn't help him for the gastelum fight.