It doesn't sound like you guys have ever played these games. Okay, maybe some of you have. But you can't play them with arcade sticks. Top pros in League or Dota have amazing mouse skills, fast reflexes, and the ability to predict what the battlefield is going to look like a few seconds into the future. This is not even to mention that both are team games, which require cohesion and strategy. You need more than 4 buttons. QWER, yes. But also the number row above for your active items and potions. D, and F for your spells. You also have various SHIFT and CTRL modifiers when you want to smart cast or standard cast. I'm not saying it's brain surgery, but please don't speak from total ignorance. If you were playing with 4 buttons, you were doing it wrong.
Do I think a keyboard is a league or dota pros most important tool? No. But yes, I do think they would be disadvantaged on $5 rubber dome versus a real keyboard.