Since both of the HMs are in trials roulette and are extremly quick and easy now (I've seen Garuda die in about 2 minutes more often than I wished to, but hey, easy exp/tomes, I guess) I dont really see what the problem with those two duties is? Why would anyone quit the game about having to do two additional HMs, easy ones like Ifrit and Garuda even...

The only thing that isnt optimal is probably the timing within the storytelling, I'll give you that - unless I missremember Titan HM is required in the MSQ for the whole deal with Ga-Bu, right? So I could see why its a bummer to be hold up at that point and having to do two unrelated fights to continue your storyline, but the same could be (and has been) said about ilvls for certain story-duties (and we really dont want to do away with those, please). So I dont see why this would be a huge quitting-the-game-over deal.
It could probably be smoothed a bit, by making Garuda and Ifrit not a requirement for Titan HM or by simply having both quests (the orignal one and the Ga-Bu one) unlock the trial, but it really seems like more of a minor issue to me. But I'll admit I havent tried queueing for either of them directly lately...