Personally, I just ran up to Helios and started hitting with combos. If you play the waiting game with him, where you run up and attack, he'll defeat you with his swinging arc attack.
Try this. Unleashe Wrath immediately. When he staggers, attack. Stay in close and pound away with whatever light combos you have. 3 or 4 light attacks followed by a heavy hit. Heavy combos are too slow. Never allow him space to use the flaming missiles. This technique worked for me on the Hard and Immortal stages. I did this without the Face of the Sun perk. Just stay close and keep him defending.