If you spend $3k on a pistol and the manufacturer says don’t, don’t. I’ve been dropping the slide since the very first time I picked up a pistol and I’ve yet to screw one up.
What you shouldn’t do is drop the slide on a loaded chamber. Extractor isn’t really built for frontal impact. That can break it. It’s designed for the rim to slip under it when the round is stripped. I’ve done it and haven’t broken an extractor yet but it’s not a normal thing. Can also cause the slide to remain out of battery, which I have experienced.
As for dry fire, the hammer is repeatedly slamming into the firing pin. Occasional dry firing a center fire is pretty harmless. Doing it hundreds of times a day for training probably isn’t something id do.
As for Mr. Wilson, I’ve seen his video on dropping the slide. In fact, I’ve shared it before. I have no doubt his guns are probably fragile enough that, as he put it, “have hammer follow by the end of a show” from people dropping the slide. Personally, I’d rather not own a gun that fragile. I can’t handle more than a few minutes of watching him myself.