YPYT is a poor mentality that at best shows you have an inflated ego, and at worst lets your ego kill your party.
The mentality is necessary in other games because tanks actually have to maintain and work for aggro there, so it's safer for the party as a whole to let 1 die while the rest live, here I just spam my AoE combo whether I have 3 or 20 mobs. The size of mob groups is more of a factor for healers than it is for tanks, and considering how simple it is to drop a healer in dungeons anyway, it's still not an excuse to kill or chastise another player. Hell, Arm's Length makes melee DPS pulling technically optimal as it gives extra mitigation while the tank has theirs on cooldown. About the only time YPYT could be acceptable is in something like Criterion Savage where it's safer to let a lone party member die than risk killing all of the party, likewise with Deep Dungeons. But even there, it still feels like an asshole move if the DPS pulled accidently.
Just bring the extra mobs to the tank, they have enough tools to deal with any pull.