Casual content the double regen debate won't matter that much, because you can duty finder queue the content with any job combination, and they design the content to allow any healer/tank/dps jobs to clear that content. While it's not ideal to same sect stuff, there are advantages to having the right healer combo/sects cause it's not a perfect world. What if people get vulnerability stacks due to mechanic mess-ups? The current dollar-store stoneskin, if either ever bothers to use it due to lack of a mitigation healer, it might not even save them compared to a nice 130%+ HP shield. It's kind of embarrassing to see healers ignore these things, all because they have a "sect they prefer". But alas, this is how you tell the good Astros form the not-so-good.

Then is double regen "powerful" when both have to heal from well behind in HP due to lack of shielding for mechanics? No. There is a reason no serious savage raid group goes double White Mage. When you are progressing with content where you barely meet the ilevel, stuff is going to hurt harder than it normally would if you were to overgear. This content you can't duty finder, it has to be pre-made and you'll take the right combo of jobs because of raid synergy.