Nobody likes losing their abilities due to level sync. It's difficult to go back to a level 18 BLM or DRG after being level 70. Not to mention incredibly boring.

A lot of the push back, though, from changing the system is that tanks wouldn't be able to hold enmity at low levels.

My proposed fix is simple: Give tanks all the enmity tools they need before the first dungeon by rearranging the levels at which they acquire abilities.

Gladiator:

1 - Fast Blade
2 - Fight or Flight
4 - Savage Blade
6 - Flash
10 - Rage of Halone - Quest
12 - Shield Lob
15 - Shield Oath - Quest

Marauder:

1 - Heavy Swing
2 - Berserk
4 - Skull Sunder
6 - Overpower
10 - Butcher's Block - Quest
12 - Tomahawk
15 - Defiance - Quest

And Dark Knight already has all of those equivalent abilities by 30, so they'd have them when they sync down. This will help new tanks understand how to generate aggro properly, and overall it'd be more enjoyable for veterans to level sync.