Whittaker weighs a little less than the average middleweight. He enters the cage weighing about 200 lbs or so. Vettori and Costa both fought in California, so we know their cage weights are 211 and 214 lbs respectively. Those are big middleweights.
Whittaker has the reach of a welterweight. He is at a reach disadvantage against 80% of the Top 15 ranked contenders at middleweight, and against Adesanya, of course.
Whittaker used to make 170 very easily. He competed as a welterweight on TUF, which meant frequent weight cuts. It didn't affect his performance, as he won that season's tournament and made weight every time. He then proceeded to fight 5 times at welterweight in the UFC, making weight each time.
Whittaker has put on some mass since then. But if dropped from 12% to 10% body fat, and lost 2 pounds of lean muscle in the process, he would weigh 193 lbs. That's how much Douglas Lima weighed when he entered the cage in California after weighing in at 170 the day before. So it would be relatively easy for Whittaker to fight at welterweight again.
