Idk why there is some odd thought process on Sherdog where NFL players can only move for 5 seconds then die.
Tons of HWs have terrible cardio anyway. I don't think every DL/OL would just automatically have bad cardio either. Joe Thomas is a HOF LT for the Browns, one of the best OTs ever, I'm pretty sure he runs triathlons and shit now. He is ripped now actually and lost weight, but was still an elite athlete at 310-320 lbs.
What if someone like prime Shaq wanted to compete in the UFC and actually trained for some years prior? On one hand it's unfair to him that he can't compete and I understand HW should perhaps be "absolute" weight arguably. But it's also unfair to everyone weighing 230-265 lbs and it's just stupid at that point.
There's a line crossed at some point. Otherwise do you want to see Cejudo or Garbrandt go fight GSP or Jon Jones? Because that's basically the gap in size we are talking (relative) between a Shaq / Halfthor and a Stipe, DC, or even Ngannou.
An in-shape Shaq with the hobbyist BJJ he has + like 6-12 months of wrestling and striking would completely rape everyone for a decade at HW.