there's something to that, for sure; there are plenty of design engineers who don't know nearly as much as they think they do, and who depend heavily on the expertise of their technicians to get anything done in the real world. they could never build an engine on their own! but there are also others who are eminently capable at the technical level, and i think their designs benefit from that

repair and design have in common that they require a lot of hard thought about the causal relationships involved in making the artifact work, tracing the causal chains through until they break, then patching them up. but they both also certainly involve other skills that the other does not; design also requires figuring out how to make new things happen, which involves imagining things that have never happened, while repair also requires knowing how not to bust your knuckles or spill the gasoline