No, you have a bad understanding.
Yes, they have more skills. Footwork, head movement, faints, precision, more creative, more technical...
Not to mention cardio.
This does not mean they can beat bigger guys.
Chris de la Rocha, a fat and sloppy HW who is 1-2 in UFC and will probably be cut off at some point, would destroy the actual FLW or BW fighters without problems.
And GSP said "if I had the same size (suddently) as them, they would beat the shit out of me"
And he is right.
Just like "if MM had (suddently) the same size as stipe, Stipe would beat the shit out of him"
Because of the gravity factor.