When you're levelling, so long as you're not trying to tank things 6-8 things higher than you, then you don't need a "tank" per se. What you want to do in that situation is spread out the hate: make sure the melee get some form of hate on every linked mob, that way a random Protect from a CNJ won't immediately draw aggro. After that, just burn them down one by one and be sure not to stand in the spawn areas if they're aggro mobs. Use Second Wind liberally. If you've got 2-3 Conjurers, you may want to figure out if one of you is on healing duty while the other attacks with Stone/Aero. Each person should be figuring out how much damage they can take over a period of time from any given mob. No hard numbers, just- "can I solo this without dipping into yellow/red health." If your parties get very large, the amount of mobs that will link will go up as well, making coordination even more important.
Hilariously though, when doing stronghold levelling at 45+, "going berserk on everything at once" will indeed be the norm.