Yer, I like Khal's idea that heals should only reduce the speed of KOs rather than preventing them altogether (unless opposing team syncs their attacks/cc together). Maybe S-E made heals so strong with a pve mentality that heal players will become stressed if anyone in their party is KOd.

I guess another option would be for scoring/medals to be based on more than just KOs alone, like additional medals awarded at the conclusion of a match to each player based on their performance. So if the team wasn't coordinated enough to get the last crucial KO but individually you made a very large contribution, that would be reflected in the final score in some way and help non-heals to carry the team somewhat.

+150 medals to your team for the 300k dps you did, +100 for 200k etc. Or whatever is a fair reward that makes a difference without throwing off the balance too much.