Hmm well imho gladiator is fine with aggro with flash spam + riot blade. 3 flashes should keep everything on you 'till it dies and the riot blade keeps you flush with mana.

Dark knight is pretty good too. Unleash a number of times equal to the number of enemies +1 and you should have them all no problem.

Marauder though does suffer some down time issues by comparison. 3 overpowers will have it all on you solid but fight too fast without goad being dropped on you and you're going to have to take a breather.

Aggro becomes an issue with Hakkue Manor or however you spell it when you go in pre-30 and the rest of the group isn't. Even this isn't completely horrible though.

The biggest problem I see with new tanks not holding aggro at low levels is they refuse to use their available tool kit to its fullest. The tanking tutorial you can take at 15 teaches you too use your aoe aggro tools once and to use your threat combo to hold aggro. That works ok when your party only attacks your target and gives you at least a 5 count before attacking/healing against small groups.