Ayy MCH has 8 times less clears on the Final Omega than Bard.

[Sylvain]

I don't think it has anything to do with the job performance overall, it's simply a matter of the job being unpopular.
I can't even recall the last time I've seen a MCH in Suzaku.

While it performs fine, it's a very clunky job to play so it's honestly no surprise.

What the above said is also true altough it doesn't explain everything as many group did clear OS12 with non-optimal group.
I've seen groups with SAM+BLM and let's be real here, you don't bring these too when you want the most optimal comp. As long as your player are competent enough, with some crafted gear DPS check aren't an issue anymore even on the first week.