Aside from the problems with the loss of sustain another often missed issue with Titan-egi now is, if you are soloing at level 70 and reach the point wherein you can summon Bahamut you are punished by losing your tank if you do so. Even if Titan-egi reappears afterwards, he has no enmity and is basically useless as a tank. If you decide not to trigger Bahamut, you cannot access a lot of your abilities since your aether stacks are tied up indefinitely until you do.