^^^Nooooo Sir, he was not.
Gaastra covered the Mork example.
Fonz was an ace mechanic, a gifted dancer, a skilled motorcycle rider and stock car driver, could affect electronics via physical force, had a degree of animal control (able to quiet a forest clearing with a “cool it”) the ability to pick up new skills almost immediately (most famously but not limited to, fencing and waterskiing, though he couldn’t master roller skating), wearing a motorcycle helmet, he rammed his head into a concrete wall and was KO’d but no concussion; he pulled a sink out of its foundations, he knocked two doors off their hinges w. open hand slaps, compared nerve holds w. a martial artist (using Ralph I think) as a practice dummy…as for fighting, bearing in mind the show runners would obv. want to keep violence to a minimum, he offscreen took out three gangsters one of which was Bull from Night Court, he and The Big Ragu from L&S took out a gang of thugs in like 2 move…I think he faced off w. The Devil once but that was more of a team effort if I’m remembering it right…there are other examples but I’d have to Google them.
The Fonz though, was not all talk!