It seems to me that people complaining about "rage quitters" are those who are playing these famously overpowered demigods, like Unclean Beast and Erebus. So, you are winning, why complain?
If I choose Regulus or the Rook, and end up playing against a team with two Unclean Beasts, I know from the start that we're going to loose. If that game would have been a custom game, I wouldn't even have started it. But since it's a pantheon or skirmish game, I have no control so I need to suffer for half an hour. And that half hour goes as expected, slow but steady slaughter. No chance in hell for a win, despite our best efforts.
That is not fun.
I bought the game to have fun, not to be a die-hard-have-no-life-online-competition fan.
If I would have quit immediately instead, I could have joined another game with better odds and had half an hour of fun instead of half an hour wasted just because you want the childish pleasure in crushing an opponent you know will never be able to harm you.
Get a life instead, and let me try to have a bit of relaxing fun between the times I try my hardest, which is actual work and family matters.