I kind of get the decision between the Maldives and the Red Sea (although as you mention, for macro, the Maldives does not present any advantages), but Cozumel is not in the same league as the other two destinations. It is a nice island and the diving is great, but it lacks the diversity of either of the other two. It is certainly no better for critters than the Red Sea.
My experience is that bar spotted eagle rays, you would have the same chances of pelagics in the Red Sea as at Cozumel. Anything can (and does) happen at Ras Mohamed! Pelagic action is pretty much guaranteed in the Maldives...
Shore diving is the Red Sea somewhat gets round the temperature issue.