When you arrive at an airport from out of Canada, you enter a common line that includes flights arriving from potentially anywhere in the world. The enhanced license is not an alternative to a passport and therefore can't be used where a passport is a requirement for all. If you are entering the US at a Canadian airport, you are not necessarily entering from Canada only. The difference with land/ferry travel is that you have to be arriving from either the US or Canada by necessity.
I still can use Europe as an efficient model: In all european airports have dedicated lanes for european passport or national ID holders with expedite entry and other lanes for all other countries passport holders and they still doing well and entry is quite fast and effecient.
And I am sure immigration officers on both sides of the borders can distinguishe between Canada and USA citizens from other countries citizens
