just recently started leveling both of my tanks since I couldn't decide and I had to facepalm several times.
Leveled up as SMN/SCH most of the time so I had no idea that tanks had to deal with some really bad dps (just running ahead of the tank right into monsters, not following the kill order, way-to-overgeared myth players, wasting stun resistance etc).
Even healers can really screw tanking at lower levels really bad, like having Eos go super whispering dawn before the pull or WHMs spamming Medica to fix scratch damage.


That said, so far, MRD > GLA in lower level dungeons. Overpower helps a LOT and I feel like it's definitely stronger than flash, combined with bloodbath, that str+ buff and maim, it's a beast!
As for GLA, I really have to rely on spamming flash like a halogen lamp every rotation, sometimes even twice or thrice right after the pull because I feel really unsafe without it. Then you just combo for the riot blade mp regeneration while throwing a flash after each combo ( or after every second depending on your mp ).

I really hope it gets better later on with Shield oath etc. But it's not a hard class if everyone has around the dungeon-designed level range and follows the simple rules while keeping an eye on the hate bar once in a while for the sake of the whole party!