Martyr Logarias, Ebrietas and the final boss (Gerhman) are all more difficult than Rom. Just poke at the spiders and dodge when he uses spells. When the spiders are dead, beat the shit out of him. Repeat.
On my first playthrough, I skipped the spiders entirely. I just beat the shit out of him while keeping the spiders on the other side of his body; he basically body-blocked them from me. I wouldn't recommend this strategy though. The positioning of the spiders and his use of spells is too unpredictable for this to work every time.