If you want to roll a tank (Gladiator) and the tanking aspect requires effort/skill/ability/whatever to handle the responsibility. However, if any schmo can tank as well as the next guy (due to mechanics), then you will leave the tanking to the kids and roll a DPS class. Hold PvP scrimmages. Getting used to open world PvP in the Abyss isn't always easy. Set up some legion events in the arena to help attune your players with what they will face. It may teach them the difference of when to stand and fight and when to run.

Actually, the Gladiator class is not meant to be used to MT, OT is perfectly fine and Gladiators are more than capable, however a lot of Gladiators needs to stop thinking is they can MT with no Shield and instead depend on parry with a Polearm. Sure you can handle elites,  you will no longer be tanking for your Legion unless you roll a tanking class as soon as you hit lvl 50 and cap.Gladiators are unable to tank raid content or hard named, Gladiators can keep high threat through their damage, but they do have the ability to taunt as early as Level 10. Templars are the pure tanks of the Warrior class and of the entire game really. Templars use swords or maces as their primary weapon and a shield to go along with it. They are masters at building threat and mitigating damage. The Templar is will be for you if your goal for your character is to tank in all situations and be able to handle incoming damage the best.