You're putting the cart before the horse. The game needs a bigger playerbase and more balance tweaks to be a sport. We're all talking about a balance tweak here. Also the mechanics of most games make comebacks way more feasible than they are in this one at the moment.
Seems to me the game is about as balanced as can be already, save perhaps 1v1 matches. Regardless, I don't see how forcing on-the-fly handicaps on players will improve balance or attract more players.
I think we fundamentally disagree on the spiral of doom thing. If anything, I would like it to be more severe than it is now. I don't want to drag out a game that's obviously decided already, and I don't ever want to feel like I just won a match because my opponents were good, but I was 'precious'. Levelling the playing field & being nice is just as much fail in competitive games, as the opposite is in society.
An alternative to your on-the-fly handicap might be to do the exact opposite of what's being suggested in this thread: nerf the rewards for killing DGs of your level, and increase rewards greatly for kills with level difference. That encourages both comebacks and more decisive victories.