It seems to me like treating QA as developers who are not allowed to write code, but can criticize it, would tend to result in a situation exactly like the one

It seems to me like treating QA as developers who are not allowed to write code, but can criticize it, would tend to result in a situation exactly like the one described. Indeed QA is not a step after development, but I'd argue that encouraging developers to become better at QA themselves is a more effective approach than having non-coders inspecting sources after the fact.