What kind of gear and skill cards do you have, and what are the specific lineups you're using for Golem and Hydra?
For Labyrinth you're probably going to have a difficult time getting further than 35 with your team. Your warrior is DPS and not Tank, and you don't have Gram, Ari, Tiel, or really any good tank for that matter.
Everyone is sporting nearly complete Whirlpool sets, and everyone is using the A rank or better Base Atk card, plus A rank or better DPS oriented gems. I'm also using the Fire all at Once formation for bosses (only lv 16 still, just bought it a few days ago). For Labyrinth, I'm using the basic Solidarity of Heart formation.
For Golem, my best results are with...
Magni Priest, Brightspark, Bloodwind, Ur, and Loki, with Whay assisting
For Hydra, my best results are with...
Magni Priest, BrightSpark, Bloodwind, Ur, Whay, and either Loki/Blackaria/Shabelle assisting.
For lab, my line up is...
Warrior, Blackaria, Brightspark, Bloodwind, and Caberra, with Whay, Loki, Shabelle, and Ur Assisting.
As for my warrior tank, does the Taunt Ultimate and 3 more levels of Defense Passive make that big of a difference? The taunt itself is pretty useless in Lab since AoE is what kills me, and I feel like an 8% reduction on my allies won't matter. I don't know if 3 more levels of the defense passive would keep me alive that much longer either. It feels like I just need another tank with invuln/stun.
----Edit-----
On revisiting the skill, from Lv 8 Solitary battle -> Ultimate, I guess I'd be adding another 20% damage reduction (plus 8% if I receive the party buff as well). That's possible big chunk of damage reduction. I also have almost no EVA, I feel like the whirlpool sets don't give any EVA. Maybe I should farm up a Valmut set instead now.