This. 9/10 bad early starts tend to turn into stomps, but that 1 game more than makes up for it (for me, anyway). I'd take those 9 games any day as long as I know that I'm gonna get my 1 uber comeback sooner or later. By implementing a concede feature, you'd be taking away that 1 game too, imo.
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As good as these features sound, I dunno - it just won't feel like Dota, you know? Every game has its pros and cons, thats what gives each moba its own particular feeling. Maybe its just that after playing the game for 6-7 years, I've just come to accept it as a part of it.