The problem with this sentiment is that, if things were actually meant/designed for mass pulling, they'd all just be grouped together to begin with. Big pulls is great, sure, more efficient, etc, etc, but every player is entirely free to play to their own style, and it's a bit of a dick move to expect/force players not comfortable with that to just suck it up to please (the collective) you. Can you really not see how toxic it is to say, "This is how we expect everyone to play the game at this point; get good or get out."?
Spamming "pull all" accomplishes nothing. Maybe the mentor could've accomplished more by actually encouraging and educating to that end. Be positive about it and you might actually get a new mass pull tank. Be a little htcib like OP mentor, and you could very well end up with one less tank in the game.