Not necessarily.
There are different skills amenable to different body types. Despite his best efforts, Matt Mitrione will never move quite like Dominick Cruz. At his weight and size, he is prohibited from bouncing in and out that effortlessly.
But, similarly, despite his best efforts, Cruz will never knock some dude out by sprawling on his head. In fighting, both of those skills can be used to win fights. There is no way of telling which will be more successful overall, therefore, we can't necessarily say either guy is relatively more skilled on the basis of being able to do something the other cannot.
The reason the heavyweights outside of the top ten or so in ranking are so much less skilled than their counterparts from 135-185 is because the talent pool is much shallower. These heavyweights get fewer fights, they have fewer sparring partners, and many of the fights and sparring rounds they do get are against fatboys with no athletic capability, where minimal skill can be more than enough to destroy a guy.
All this to say, the best heavyweights are just as skilled as their smaller counterparts, no doubt about it. Just with different skillsets. However, below the top ten (or so), the heavyweight talent pool becomes so shallow that many 205s and 185s would absolutely run roughshod over them, and the heavyweight fetishism has to be reigned in a little bit.