Bivol is meant to be a natural 168 pounder. Smiths size did nothing for him in his fight against the smaller but much more technically skilled Bivol , so there goes your argument that size the the single most important factor in boxing. The fact you have to match 175 pounders against fully fledged Heavyweights proves your points are rubbish.
Loma is definitely a featherweight, and that may be why he had a subpar performance. But he still won 7 rounds in my book. Lopez is the basic fighter, not Loma. If Loma was a basic fighter, Lopez would have knocked him out.
Why do you think people cry so much about a few lbs? Of course size is one of the biggest factors in the sport. Size can't overcome every other factor. Size without ability to use it as an advantage is pointless, but a big size advantage when the fighter knows how to use this strength can easily overcome a big skill and ability advantage. I'd say a bloke off the street like Kimbo would beat a Rigo easy. Kimbo has very little skill but he would be able to use his size to win the fight.