The best QA people I've worked with were effective before, during, and after implementation - they worked hand in hand with me both to shape features testably, work with me on the implementation for the harness for additional testing they wanted to do beyond what was useful for development, and followed up with assistance for finding and fixing bugs and using regression tests to prevent the category of error from happening again.

At the very least I want someone in QA doing end-to-end testing using e.g. a browser or a UI framework driver for non-web software, but there's so much more they do than that. In the same way I respect the work of frontend, backend, infrastructure, and security engineers, I think quality engineering is its own specialized field. I think we're all poorer for the fact that it's viewed as a dumping ground or "lesser"