Every good competitive game I can think of allows for huge comebacks.
Allowing for a comeback doesn't mean it has to be easy, and the advantage that was gathered by all team members should get easily lost by a single mistake of one member. It's easy enough to lose a game, despite your best efforts, because you just happen to have a fuckwit in your team, or someone disconnects. It's not fun.
Frankly, you SHOULD lose if you have a fuckwit in your team, and the opponents don't have one. That the fuckwit makes a stupid mistake and makes you lose a won game is just a result of playing in pick up groups, par for the course in a team game. If you don't like fuckwits ruining your wins, play a 1v1 game instead, and rage at yourself. In any case, competitive games should not be balanced around what happens at low skill levels, they should instead strive to be as deep and fun as possible at the very top.
Yes, but what I meant to say is that relying on a build up of power, rather then constant balance and need of extreme awareness (this is what I'm getting from you, I know nothing about dota experience, but I'll try to change that), allows you to still win in unfavorable situations like 4v5, which are bound to happen from time to time, IF you're good enough. I think it's a good solution for limiting the effects of those technical issues and random retardo moments. It makes for a good experience without compromising the skill necessary to win in any way.
And you can still fuck up majorally because of a single mistake or CC. It's less likely in casual play, especially before late-game, but at professional level games are mostly won whenever a single mistake is made. It's pretty hardcore, I'd say.