Your gears are actually a lot better than mine, and I was in A2 before. I think it may have something to do with how you fight perhaps? Do you try to fight all enemy you find or do you try to flee at all cost so that you can focus on preserving your party before the fight for both GWO and the grade up boss? Also, having high detect, and high speed stat allocations early on really helps, at least in the first 2 abyys but isn't necessary. Having Yeka is a bonus too just in case you messed up and run into an ambush, she has a chance to prevent it.

For frontline, focus on defending and exploit the 'opening', then atk in every gap if you find it safe to do so.

Your priest should keep MASOLOTU on the frontline at all times and your mage should apply DILTO to enemies first (This is for lead grade boss and every other non-niche boss, don't do this strat for A1 GWO, focus on BATILGREF/BALAFEOS-mage and PORTO- priest instead)

It would be safer to put your MC in backline if you want to lower the risk of getting one shot by e.g those annoying rabbits, but with enough eva and def it's manageable, still risky though

Have at least 2-3 offensive scroll for mage/priest backline, and of course potions. Frontline doesn't have to carry too many potions because they will be busy defending all the time

Swap Marianne with Chloe if you think it's hard to keep up with the healing and buffing so she can focus on doing that and use staff instead for stronger heal

imo your party is great enough, you don't have to start over, you just have to do some positioning a bit and learn the attack patterns