And all I'm getting at is that, to me, I feel far more mobile on my other healers. That doesn't mean I like them more. I deleted the Sage at 33 and perhaps it would feel different at 50. It was so squishy it had to be, I'd often bubble and force sprint away from danger. In contrast, my Commando felt very durable and while leveling I would often "heal tank" mobs with a DPS pet. I didn't feel the need to move, so I didn't.
Obviously at end game you have to move for mechanics in Ops, but the encounters are designed around it. I haven't raided since I've been back, so my examples are old, but on Soa they gave plenty of time for Salvation on the platforms to counter the ability of Commandos and Scoundrels to AoE while running.
It's true that in most Ops you have plenty of time to stop and cast even on movement phases. I've never had an issue with that on *any* healer, and I've played all 3 at 50. Merc is my favorite, but that's due to preference of playstyle, not because I feel it's "better" for some reason.
The reason I have issue with that description of the class as a turret healer is because I see people talk about it in the sense of Operations and similar things, or in Warzones, etc. Leveling is an entirely different ballgame, and yes, you can feel like a turret there when playing a Merc, no matter what spec you're in.
At 50, in Ops, all 3 classes are mobile enough. The Sorc does still suffer the most in movement phases in raids as far as being able to heal on the move, but they make up for it by being able to Force Speed when they need to get to a spot quickly. There are no operations bosses currently in the game that *require* you to constantly heal on the move - at most you'll need to move for 3-4 GCDs and try to keep up heals, then you can plant and cast with any class. In *those* situations, in my experience, Operatives and Mercs are best suited to actively heal at those times. Operatives more than Mercs, because they don't need cooldowns to do so.