He can save a teammate. The healing power is not reduced at all. Koschei dies under focus. Great, just like every other ship. The problem is, other ships have to be visible, and with the recent changes, are in range of at least one type of ship. Not with the two healers. They usually hide beneath terrain or their own ships, which makes it nigh inpossible for any large ship to get a firing solution on the healer. The Aion is not that as much of a problem because of its limited healing power, but the Koschei basically makes a ship near invincible with shields, and take much longer to kill without.
Hiding behind terrain was always a thing and the range cap didn't change a thing about this.
Your team needs to git gud or you're lost against a decent Koschei. Simple as that.
No teamwork, no reward.