I trained my girls to lvl 40, did some Via Infinito, and went back to Angra Mainyu killing.
I used different strategy this time around, I sacrificed my attack stats, but instead got def high and status def. I went with 2 Alchemists and 1 Dark Knight. I decided I would drain mp with Alchemists using mana springs, it's very fast way and then switch all to Dark Knights and pummel it to victory, doesn't worked quite like planned. I ran out of items before I drained Angra's mp, it has way too much of both MP and HP, insanely high. Anyway, using attack items (not mixing them) is very fast. So in case someone had 99 of mana springs and 99 Supreme Gems (lol), it's possible to kill it efficiently at any level with 3 Alchemists (and you don't need to care about inflicted breaks too), well, not at any, above 1k HP is still preferable for this fight.
It took me 2 hours to take it down, it finally ran out of MP, but it was very long until it did. I used almost all my useful items, but at least it's dead, finally.