I'm not small. I'm 6'1 and 240 lbs. I've trained a lot of judo, wrestling, and BJJ, and a small amount of muay thai. My experience has always been that the smaller guys are more often than not more skilled than the bigger guys - yet the big guys still beat them because they are bigger and stronger.
Heavyweights are able to get by on knockout power, or by manhandling others who are smaller than them. This leads them to develop less actual technique than those who do not possess that same ability. Take a guy like Derrick Lewis, or Francis Ngannou - both are guys who don't have any sort of amazing technique in their striking, nor do they possess great grappling skills. But due to sheer physicality and power, they can climb to the top of the heavyweight division. The higher weight classes quite clearly have more one-dimensional fighters than the lower divisions, and that's because when you're big, you can get by on physical attributes more easily (i.e. insane knockout power). If a guy like Islam Makachev, Alexander Volkanovski, or even Sean O'Malley possessed the same physical attributes as Ngannou or Lewis, they would utterly outclass and brutalise them. Those smaller fighters are infinitely more skilled than the top heavyweight fighters in MMA. I think you're fooling yourself if you think otherwise.