HM Titan is absolutely a gear check. Denying this helps nobody.

Tanks need HP to survive Mountain Buster
DPS need dmg to break Heart
Heals need magic to heal Tumults.
You need to end the encounter before the stacking Tumults become too much to handle. Nobody can survive this fight indefinitely.

Can one person in the party survive Tumult with 1500 hp? Sure, with extremely well timed heals, including using Swiftcast, etc..but he is not carrying his own weight in the party and therefore would never get invited to a group.