It seem that after all the long winded discussion and all the debate, the bottom line is people don't like to have everything riding on instant kill gimmicks.

Well consider titan. How about we throw on RNG into that instant kill move, maybe 30% of the time, in exchange for a player being knocked off, the player is feared/stunned/hysteria/whatever and titan gains back 1/8 of its health for every player hit. And if the health goes back over the 50% you go back to pre-heart phase.

Would a simple change like that be acceptable?

If so then you can extrapolate this into many of the other 1-hit kill mechanics in any other dungeons.