I guess it depends on what "A", "B" and "C" means exactly.

But the problem with "C" managers is that they won't judge "A" work as "A" work, won't understand why some of the "A" work is important, and will get in the way of the "A" engineers, making them go down "C" paths.

A "C" level manager brings the whole team down to "C" level and destroys the morale of "A" and "B" workers while they're at it.

An "A" level manager can guide everybody towards "A" level work.