My experience has been that a good project manager is critical at defending against other teams' (bad) project managers. The other PM's can cause a lot of trouble if they're politically saavy.

This applies to business analysts, scrum/agile people, communications people, and other non-technical project staff, too.

I've observed an arms race at play in my department. Our team used to be 4-to-1 developers to business people. But we've increasingly needed to hire more business people just to defend ourselves against political scheming.