Guy Chamberlin
Heisman Trophy Winner
A system quarterback is a marginal player. He relies on the talent around him, for the team to be successful. He has limited skills and is replaceable. The next QB will do fine too, as long as there is really good talent on the team.
The second video is literally saying Crouch didn't have many options around him. It was run, pass, scramble, make a play. And he was extraordinary, like most great quarterbacks.
As mentioned, Patrick Mahomes was a system quarterback. His system gave him inflated passing numbers, which discounted him for the Heisman but worked well enough in the NFL system, although plenty of other college air-raid QBs flamed out in their pro careers. There are only two "systems" people seem to talk about in college: dual threat option and pocket passing air raid.
Some have argued that every Alabama QB is a system QB in that they only had to be efficient because everything around them was so good. Definitely some truth to that, but I wouldn't call those players "marginal" or easily replaceable. Actually not sure I understand your definition of system QB. You seem to be talking about mediocre QBs who still win games because the team is good. I don't think those teams go out scouting for mediocre QBs.