In my opinion Ultima is about the same difficulty as Titan HM in terms of dodging mechanics, but given a decent WHM/SCH it is far more recoverable, so in that sense, it is actually much easier as a group, even if not as an individual.

Titan you lose someone to landslide, they are out for good. Further due to the timing of stomps, you are very limited in ability to raise those who go down to WOTL, and you have to rely on having a SMN/SCH do it.

I have had to raise more than 3 times as WHM over the course of an Ultima, and use LB3, and still finished in time, without running out of MP when it mattered. On titan, more than 2 raises and it is all over because I will run out of MP and not recover enough in time.

If you find Ultima easy enough, you should be fine on GEX though.