Is the "timing your rush to run in when the play clock hits zero" really a thing? Like, I don't see DL looking at the play clock, they're looking for the movement of the ball or the OL. LBs are more upright and could conceivably see the play clock, but they're usually looking at the offensive alignment. When a team does get a delay of game penalty, I don't see 4-5 guys on defense just coming across the line when the clock hits zero. They're usually as clueless about a delay of game penalty as everyone on the offense other than the QB.
I get it causes angst when you're watching the game, because we don't want the penalties, and it seems like an easy thing to avoid, especially when the offense is lined up with 10 seconds left or whatever. But I think the "defense teeing off" argument is bogus.