It’s not just about the character being technically capable, but the player being comfortable with it, because a lot can go wrong when you’re pulling several tens of mobs. It’s easy for a few to escape and go wreck the healer for example. If the tank isn’t confident in their ability to hold threat on a small city’s worth of mobs, they shouldn’t and should scale back to what they’re comfortable with (which might be 2-3 packs at a time instead of half the dungeon).
Also I wonder where this obsession with speed is coming from. Everybody’s acting like they’re gonna be the hottest cutting edge raider and have to have full BiS yesterday when obviously only a small percentage will ever achieve anything close to that. Seems like a streamer-induced mania of sorts.