Engineer B who can get that over complex solution working is the person you will turn to when complexity is required for the problem. They have experience in getting it to work, and such they really are worth more.

The real question is how do you tell engineer A who can figure out how to make the complex problems simple from engineer C who can't handle complexity and so writes simple solutions when the complex one is needed.

Not really, because even when complexity is required, the last thing you want is even more, unneeded complexity. There is no guarantee that the kind of complexity B brought to a problem is the exact same kind you're going to need somewhere else. It turns out that complexity is, shall we say, more complex than that.