Or also, unbalanced because the whole game is based upon overpowered skill, items and heroes rather than teamplay and strategy.

Most people try to avoid playing with their allies, as it slow down XP rates. You just wait behind your creeps and cast a spell from times to times, until you have enough money to buy some flawed item. Rinse and repeat until you're powerful enough to one-shot a tower or another hero. End of the game.