What am I doing wrong with my GLA?

[dramamine]

Since nobody else pointed it out, provoke's description in game is misleading.

The only thing provoke does is set your current enmity level to just above the current highest enmity value on the enemy's enmity table. Or in other words, if the current target of an enemy has 2000 enmity and you have 1500, provoke instantly generates 501. If the current target has 2000 and you have 2000, provoke generates 1. So the best way to use provoke, especially once you get RoH, is to queue up a combo attack (savage blade or especially RoH once you get it), and use that attack right after provoking to give you a bit of a cushion. Also, never use provoke on an enemy that you already have hate on, since it's a complete waste (even if it generates the same as other off-GCD abilities like FoF or Rampart, it's not going to make enough of a difference to be worth using, especially if having to wait 30 seconds to use it again means that you risk not being able to get the aggro back).

All of your enmity generating abilities generate enmity proportional to the amount of damage you do, including flash. The problem you're running into is that you're winding up in dungeons with DPS/healers that significantly outgear you, but don't know how to manage their own enmity generation. The best way to minimize the trouble that causes is to choose your gear/allocate your stat points to maximize your damage output. As an approximate rule of thumb, 1 weapon damage is worth roughly 4 str, and 1 str is worth roughly 4-5 secondary stats (which aren't going to accumulate to make a big enough difference at your level, so you can really ignore them and focus on str).

This means to get any empty slots you have filled with str gear, then focus on upgrading/spending the most gil on your weapon, shield, chest and legs. If you're using NQ weapons, you should upgrade them as often as possible. With HQ/aetherial/GC/dungeon wepaons, you can probably get by with every 4-5 levels, and that's definitely the thing you want to buy first if you can only afford one piece of gear (since the extra weapon damage is going to trump any benefits you'll get from other gear slots). low level STR materia tends to be pretty cheap on the marketboard, too, if you can find someone willing to meld it for you. That can help extend the life of some of your LQ stuff for a few levels.

If you don't have the gil/seals/crafting abilities to make gear for yourself, leves are a good way to level for a little while. You'll get a chance to get some aetherial gear, gil, and company seals. Additionally, even if you wind up wearing NQ gear from quests that's a few levels behind, once you're level 40 it won't really matter. You'll still max out your stats for level sync'd dungeons, and you'll have shield oath and more abilities for the higher level dungeons. If you enjoy tanking, keep with it, it does get easier.