I mean, I don't know personally. I actually fit Snow's description of a SCH main (will flex to all other healers but prefer AST the least), though I more consider myself a WHM main, personally, there's probably something to that.
I feel like a lot of people will flex to a second one, but not necessarily any more than that. My experience with PF is that I'm often the only Healer that will or even can flex. Others often don't even have a second Healer Job leveled. Though most who have more than one have WHM + something (usually SGE), and are okay swapping between those if it's needed, though they don't prefer it.
I feel this is a case of the company you keep, maybe. Like I'd guess you tend to run into a lot more hardcore Savage/Ultimate people whereas I tend to run into a lot more low-to-midcore Savage/Extreme/toe dipping people.
I can play all Healers that aren't AST in any content. I can probably play AST in Extremes, I just feel competent with it and over-weave all over the place in the burst window. While that's PROBABLY only a negligible damage loss, it /feelsbad, so I stick with only doing 4/24 mans or 8 man normals with it when I get the itch, which isn't often.