I don't think I understand the analogy? If two people are working on the same project and one enjoys and specializes in front-end development and the other enjoys and specializes in back-end development, and the project is roughly 50/50 front-end and back-end, why on earth should they NOT split up the project accordingly? They will both enjoy working on it more, they will get it done faster, and with better results than if they each took half the front-end and half the back-end work. Neither partner is "exploiting" the other or anything like that (as implied by your analogy); it's just in their mutual interest to divide the work in this way.