For the slime boss, you will have to group them up around the bombs. Blobs not in the bombs will not split, prolonging the fight. I wouldn't worry about damage though as the attack power seems to be divided amongst the blobs. Smaller pieces deal significantly less damage than the big slime at the beginning. If are having trouble surviving all the hits as a gladiator, you might consider gathering the mobs so they're attacking you from the front. This will let you capitalize on the block stat from your shield. Otherwise, get lvl15 gear for you and your healer. You should not have any problems after that.

there's two tricks to the final boss. The first is to go all out on dps with the boss and ignore the adds. In this strategy, your conjurer/arcanist is encouraged to contribute by activating cleric stance or using emerald carbuncle. Overall, this strategy is fine if you have a healer not prone to panic and capable of healing/dpsing on the run or a thaum who can sleep enemies if your group does panic at the 1-3 mobs that might break through.

The other trick is to tank the boss next to the second opening. Since the adds don't initially aggro on anyone, the dps can safely attack them. By having the boss near where the adds are, you allow for your casters to utilize their aoe and your melee dps to quickly kill the adds and then attack the boss. This is the more technical (and i believe intended) of the solutions.