I can usually burst down Bahamut before he starts his big attacks, but it depends on a lucky crit or two, or if server ping doesn't like me that day. Give it another patch worth of gearing up and that'll smooth out.
Most of Heavensward is pretty soloable now too. A couple of the Alexander Savage fights are rough if you're not on a tank. Sephirot has to be burned into his phase change before he gets off his tankbuster, otherwise it stacks a vulnerability debuff and crushes you, but it's doable. Zurvan just stops taking damage at 1 HP until he drops the platform to end the intro phase, but he'll die immediately from an auto attack after that. Sophia's biggest threat is tilting the platform to slide you off. Thordan, Bismark, and Nidhogg are just time-consuming. Ravana is pretty easy to nuke down.