What evidence is there of that? Dropping Bader? Hardly reason to believe he's a massive hitter. He wobbled Rampage, but Rampage had been rocked/KOed before; I don't think his chin improved by the time he fought Glover, he just got better and not getting hit clean. He hit the Iron Hillbilly with everything but the kitchen sink and couldn't get a finish. So who else did he KO that is worth mentioning, whose chin we know is iron?
Stipe, a guy who was accused of having pillowfists for a HW, knocked Fabio out in what, a minute? Took 10 minutes of brutality to get a mercy stoppage when GLover fought him. Rampage couldn't take Fab out, either, and he had 15 minutes. Glover doesn't have elite HW power, or if he does, he hasn't shown it so far.