That's a lot of money, however a handful of fighting games and other RTS's such as starcraft deserve more prize money in their respective toruneys simply off of game design principles and the amount of discipline required imo.
Not really. MOBAs tourneys deserve that money far more.
Any game where grinding is a requirement is automatically disqualified from that statement - the amount of time you play shouldn't directly improve your chances of winning. Only tedious practice should win a game.
There is no grinding in Dota. Team fights can and often do happen at early levels (especially in higher levels of play). Even as low as a level one Rosh attempt.