I wouldn't turn off shadows completely because they add depth to the game, but maybe you should turn them off for the enemies only? If you still want a shadow like appearance then maybe you make a small blob shadow texture on a quad beneath the enemies to give the illusion of a shadow. Because it's directly below them and centered, it might make it less difficult to judge where the enemy's hitbox actually is.
No idea if this would actually work, just something that came to mind and I think is worth trying out :)