Sophie and Cheria are the two primary healers and do play (and heal) differently. With the way CC + Casting works, they really do end up functionally different due to how they approach combat. And I'd contest that both the Graces healers aren't completely screwed over when enemies look at them; I really haven't had that kind of issue on Chaos at all except fluke double/triple simultaneous deaths.
Hubert's spot healing is pretty shitty but, like Sophie, he'll combo a lot so it's basically an instant small area-of-effect heal; Vital Flair when fully upgraded is a nearly 50% self-heal off a 3->4CC A-Arte so it comes in handy.
But I didn't really have a good outlook on Vesperia's healers that you seem to. I never gave Karol a shot (since I hated him) and Raven always felt inferior to Estelle so I just stuck with her despite the fact I didn't like her; just "dealt with" using Raven eventually.
While Sophie and Cheria
play differently, I don't really think that they
heal very differently at all. Sophie is better at single-target healing and Cheria can do a bit better for party healing, but they're still just spells with standard cast times. You can shorten the amount of time it takes to cast by chaining A Artes into B Artes, but a) I don't think I've ever seen the AI actually make use of that, or if it is, then it's not enough of an effect to really change things, and b) shortening the cast time doesn't really help matters if to do it, you need your healers to be close enough to attack in the first place (that is to say, taking two seconds to heal when the enemy can reach you and attack you in one and a half seconds isn't functionally different than taking one second to heal if the enemy can reach you in half a second).
When you start running into bosses that can absorb most of a combo before they'll actually stagger (so you only delay them for 20-25% the length of your combo), who can't be knocked down by moves that are made to do knockdowns, and who two-shot any of your characters from full health, it's easy for it to turn into a matter of having the boss run around killing people as fast as your item cooldown can throw out Life Bottles, hoping that you'll get lucky enough to stabilize the party condition before you completely run out of items. Going on the offense doesn't really help since you can't keep the boss staggered and disrupted enough to stop him from going after your healers, and going on the defense can literally mean switching control from one healer to the other, canceling their heal spell to dodge, and then having to switch back to the other healer to cancel
their heal spell to dodge, ad infinitum.
The healing in Vesperia was far improved. Each of the three healing characters were best suited to a different sort of fight, and if you doubled up and brought two of them in the same party, they didn't share the same counters the way that the healers in Graces, Abyss, etc do where it's all done via spells.