You're correct: correlation != causation. Marcelo not lifting weights doesn't imply it wouldn't help him.
Which is to say: you seem to have missed the point entirely. The point is that people like the genius I was responding to have no idea what they're talking about when it comes to preparing for elite competition. Would lifting weights help the average competitor? Maybe, maybe not. I didn't take a position. Do the people on this forum, including me, understand the intricacies of muscle repair and maintenance, of neuromuscular innervation, of metabolism? No. The most learned scientists in the world don't really understand such things, and that's why so much medical advice boils down to, "do what makes you feel healthy."
As you implied, it's impossible to do a randomized, double-blind, placebo-controlled trial (the gold standard in proving causation) in cases like this, so we're stuck with the above, woefully incomplete science. We're in a sad state when the experts are dramatically less confident than the laypeople (oh, excuse me, enlightened grappling masters) of the Sherdog grappling forum.
That's why posts like this are so silly and wasteful. And since I don't suppose this message will get through your thick skull, I'm going to do something more productive now.