If project Managers are hired to control costs, and technical specialists work in silos, then who carries the products through the project?
In many cases the answer is no one.
The executive needs to work with a project manager early in order to identify outcomes and project tolerances (BEFORE the project begins or the budget is set), and then make THAT the main focus of the project manager.

Tolerances
Far too many executives leave this up to the technical teams, and then bring in a project manager to act as a project administrator for reporting purposes only.
To make matters worse, if outside experts are brought in to deliver, then why do organizations often prescribes how these experts should do their work? Doesn’t this beg the questions “why hire experts in the first place if you don’t intend on learning from their expertise and experience?”
Could it be that too many experts don’t know how to deliver value, or is it the organization that doesn’t know how to receive it?