Also, there's a huge difference between teams where QA is seen as a stepping stone on the path to graduating into "real" development, versus teams where QA is viewed as a critically important role that's valuable in itself. There needs to be a role for senior QA engineers, because if all your junior QA folks are looking to "graduate" to development you won't get expert QA folks who really care about QA.

I've seen what great senior QA engineers can do. Proactive approaches to testing; integrating new approaches to testing; influence on architecture and design to make codebases more robust; optimizing testsuites so they can run more often; better capture of long-tail errors from production; design and implementation of scratch infrastructure to test more things before production...