Yeah, as it turns out, the human brain just isn't very good at controlling two birds. I kind of shot myself in the foot with the concept, because even with some practice, two birds ends up only being somewhat more efficient than one, so any easier and you can just obviate the need for one of the birds in several levels.
My biggest takeaway from this jam is: Try not to make games that go against the human brain and nervous system. I realized pretty early on that this was going to be incredibly hard to balance, and decided to kind of live with it, but I should probably have retooled the concept before I got too deep in.