There's no way to measure how useful a heal is in this game. With the abundance of Tac Teams on ships shield-heals aren't that useful for most - and it's not like everyone doesn't have Hazards or Engineering Team to fall back on even without a dedicated healer. So I'm not sure how someone who just wants to primarily heal should be considered a huge asset in a Fleet Action.
For example, if the game were set up differently where Escorts had zero access to heals - or if there were some type of real penalty for dying - then a healer might be worth more, but as the game is right now there's no way for healing to be as useful as damage.
STO is about my Liberated Borg Federation Captain with his Breen 1st Officer, Jem'Hadar Tactical Officer, Liberated Borg Engineering Officer, Android Ops Officer, Photonic Science Officer, Gorn Science Officer, and Reman Medical Officer jumping into their Jem'Hadar Carrier and flying off to do missions for the new Romulan Empire. But for some players allowing a T5 Connie to be used breaks the canon in the game.
I like the idea, but the execution seems inconsistent. I've gotten first with monster DPS builds and mule ships, other times those same ships don't even place. For example if heals only against actual damage help, then damage-mitigating abilities like EPTS or the Engineering Fleet cost you opportunities to score. If only hull damage counts then the heavily-shielded Tholians are a trap. Stuff like that. I don't know if its unfair so much as unclear.
So far... best I've done is 3rd on my Engie Escort (using Phased Tetryon) as well as my Sci (Which uses Phased Polaron). My Luna class isn't a DPS boat by any means, but she was dishing out the kinetic with Grav Wells, Tractor Beams, and Tractor Repulsors. Throw in the occasional Subnuke beam and I did pretty well. Swapped out my aft torpedo for a Bio-Neural warhead... Don't think I did as well...