Right now the only issue with healing is that the Koshei's healing output and armor make it the obvious go to option for most teams who have access to it. While yes, good corvs can still take one down, against a well organised team that's highly improbable (not to mention the skill of the healer playing into this).
The fix? Simply give the heavy repair beams to the Aion, and the medium beam turrets to the Koshei... easy fixed. This means that a good Aion captain with a good team can still dominate, however the healer is vulnerable enough to corvs and artys that it's not an overpowered combination. On the flip side, they can use a Koshei and be able to rely on the higher armor and defensive ability of the turrets to survive assaults from artys or corvs, but give up the high repair capacity in exchange.
(As an aside, Destroyers are balanced this way, why aren't the Tac Cruisers?)