The right person for doing QA for code written by developer A is developer B, who is motivated to show that there is breakage in the code written by A. This is just good old peer review, in the sphere of development.

The industry uses dedicated QA people based on the assumption that you can get two for the price of a developer.

In fact, if you have two developers, one of whom is more clever than the other, you want to give the code cranking to the less clever one, and use the clever one to verify the code cranking and make improvement suggestions.

If you have clever people designing the system, and clever people finding problems in the commits, you can just have average coders cranking out the bulk of it. Most code doesn't need cleverness, just persistence and consistency.