Why do you want to correct a character that you consider overpowered by buffing other characters of the same class ? This is not logical. Better nerf the culprit instead of buffing the three others. Especially since other medics are considered balanced for most players around.
You also overlook Spark’s major flaw : her healing is very weak. This is compensated by the REVIVR, allowing her to revive at range while acting like her real primary weapon. Basically, if SD gave to Sparks a superior way to revive it’s because her healing won’t allow her to sustain the team unlike the three other medics. Spark’s issue in pubs isn’t her ranged revive.
If there’s something about Sparks to be really upset about, it would be more the fact that she can patch herself up almost instantly with her small medpacks. Couple this with the fact that Sparks is very fast, and you get something really frustrating to fight against in pubs. Catching a Sparks is already pretty hard, but with those small medpacks she tosses at her feet while fleeing, you are pretty much forced to get rid of her in a single hit. This can be fixed easly. Just make it so small medpacks can’t heal its owner instantly.
Spark’s main flaw also tend to totally disappear as soon as you enter a competitive environment with friendly fire active : a Sparks can just kill a low HP ally and revive him just after with the REVIVR. This beats the purpose of Spark’s main flaw, but it does not apply to pubs.