It's easy to solve this concede argument with the following system (note that it's only an example that with deep and meaningful thoughts can be improved even further):
-Teams that destroyed a lane's raxes will get extra point if they end the game shortly after that.
-If the losing team lost one or two lanes' raxes and still manages to defend and fight with " pride and honor" resulting in a prolonged game after they lost 1 or 2 lanes
, will lose less points with the loss. (Hm, help me with this one. Try to think of something else or an addition to this!)
-Leavers are punished. No excuses.
-Griefing is punished. (I think there's already means to report griefers, right?)
Another thing that I want to happen is that Valve, Dota 2 itself and players emphasize on how losing couldn't be a bad thing.
See the example above: If you defend and stay true, trying to use the best out of your team even though you are losing and YOU KNOW you will lose. You will get a "softer" loss, or in fact shouldn't even count as loss. Now, people who go fountain-afk, griefing and trash-talking indeed should get a loss marked on their stats.
Just my opinion.