It's different in striking sports where a 220 HW has the combination of size & speed to work most slow bodybuilder types. But in MMA giving up 20 pounds at 220 is a different ball game.
Sure Fedor was 230 in his prime and CC as light as just below 220, but those guys were strong enough to mostly get the job done despite being taken down every now and then and had the speed & skill edge standing. DC's undersized and overweight as a HW, but has the wrestling to not get BF killed when that dude gets on top. So you need to be much more skilled or have Manhoef power and play the matador if you give up size.
Those 3 guys are exceptions, while Chuck, Randy, Rumble, Gus, Jones, Glover, Davis, Rampage, Tito and Rogerio are the rule.
Randy struggled with big grapplers.
Rumble barely got past AA, who at the time and now isn't a great HW, while Rumble's a great LHW.
Rampage didn't want to fight Sergei because of size and Barnett did what he wanted to him when sparring. Took him down and kept him there.
Jones has still not fought at HW despite years of talking about it. He agrees that the bigger guys could give him trouble.
Size makes a difference in wrestling and grappling more so than in striking (using reach or negating it being a main thing with it), and bigger framed guys take a better punch on average.