I don't think this is black or white. I've found out that brilliant engineers actually can be incredible people managers if you help them develop those soft skills. Sure there is the age old adage that "I am a brilliant engineer just pay me more for my engineering work" but this has two aspects. For one you definitely can do it if your org is big and rich enough. But on the other side, software is a product of people interacting. If your engineering importance rises you still will have to deal with lots if people. So are you really staying purely an engineer then?