People have underestimated Chimaev's wrestling for some time.
As he didn't engage with BJJ black belt Burns, people said stuff about Usman being a true WW, impossible for Chim to hold down.
That Burns having fought at LW at one point proved how a true, elite WW in Usman would have no problem staying up.
Now, things do get harder the heavier guys you fight. But it's not like the technique and grip strength just vanishes. He's always trained
with MW's and LHW's and no doubt Whittaker is the biggest test of his career, but it would be dumb to say that it's gonna play out all on the feet.