It's important to understand that League of Legends and DotA are MOBAs — slightly different in terms of dynamics, but they are far from projectile dodging. WASD movement gives more control over the character and makes it easier to dodge enemy attacks. You could certainly make it a user-selectable option, but I think most people would choose WASD because it's more familiar to them.
As for balance — it needs to be worked on throughout the entire game development period. Otherwise, players will start asking: Why should I use other progression paths if they're clearly weaker?