You're missing the point. It isn't to argue that pavement alone immediately neutralizes all advantages of a wrestling skillset. It's to highlight that the environment itself can negatively influence the nature of skillset advantages. Suddenly not everything is in the cage. A hard ground material is a relatively insignificant factor. Far greater considerations in a street fight, for example, are the circumspect assumption that you will potential suffer mutliple attackers. This is one of the reasons groundfighting is just a bad idea in the street. So you took one guy down, you've got top position, great. You've sacrificed mobility and put yourself in an easily assailable position for a second attacker. Maybe the attackers have weapons. Once again, this isn't king of the beach stuff. You can't assume honorable 1v1 combat. Mobility and range are far more valuable. This is why suddenly the self-defense aspect of martial arts shifts in favor of striking disciplines for a cautionary practitioner.
Furthermore, it's not the trained guy's ability to stomp that was the concern. It was the untrained guy's. You can argue the theoretical advantage for the smaller trained BJJer to gain a dominant position, but that's moot. The point is that smaller guy will much more easily neutralize the larger guy's advantage in the gym fighting from the bottom. Passing guard requires skill. Stomping-- not so much. So none of those bottom fighting strategies are advisable in a street fight because that guy can suddenly kick you in the head. He can pick up something lying around nearby and hit you with it.
The truth is there are weight classes for a reason. This is an inherent handicap system ingrained in combat sports. While smaller guys with highly proficient skills may overcome a great deal of their size disadvantage, it remains a massive disadvantage. Think about it for other sports where they don't handicap. You can train a 130 pound man for his entire life as a lineman for American Football, and I'm sure he'd be a highly proficient blocker. But put him against a 250+ pound monster, and much of his skill won't matter. Then take away rules of conduct on the line, and now his life is that much more difficult to deal with his size disadvantage. Similar principles for a fight.
there are weightclasses to seperate trained people from one another.
You're correct, if you take a small person and a large person and have them ram into one another in close quarters the large person will win. However, if the rules permit that small person to move out the way, attack ankles, knees, hips, climb the larger person, etc. it comes down to who is more skilled and savvy.
Like I said, if you can point me in the direction of an influx of videos of smaller grapplers in street fights who are getting stomped out on pavement, kicked by multiple people, etc, post them. I have been in a ton of street fights, I have been jumped by multiple people, I am like 160lbs on a fat week and I am telling you, the average person has no clue what the fuck they're doing and it gets even worse when there are more idiiots who don't know what they're doing involved. Bigger guys gas and fall over so easily it's pathetic.
I have a bluebelt that's maybe 5'10 170. Judoka, jiu jitsu, mediocre wrestling, don't even know if he can throw a punch.. I would take him over almost anyone who isn't a pro athlete in a street fight, don't care about their size. If they lay a hand on him they're getting fucking shellacked in ways they can't even get their heads around. Grass, pavement, water, don't care.
All these variables of like "What if there are multiple attackers???"; dude, how deep into this are we going to get? Guns? Bottles? Knives? Pool Cues???
Grapplers at an intermediate level have an advantage over almost anyone in a street fight. Not disputable.