I always blaffed by two things : first it's how people love to push games to their limit, 2nd is how people love to take everything that can help their opinion in account.

Also people tend to be very strict on what should be. I don't think SE bothers if their content are done with non standard group. I could even bet they like this, because it show how imaginative et determined their community is.

And let's be serious a bit :
-Have Healer to have a somehow complex DPS rotation will not help the role.
-Have healer to be forced to spam Physicks/Cure/Benefic/Diagnosis all the time will not help the role neither.

I've always found FFXIV encounter are designed more like a puzzle challenge than like a brutal tests of skills. Considering this, having mechanics which need two healer or two tanks for the sake of healer and tank needed to soak them somehow is normal, fun and engaging.