Working at a very small place in house QA was absolutely impactful in being subject matter experts on what the software actually did and was supposed to do. I am not sure how you measure that.
A good QA might be even the folks that know most how system actually works and what are all the features. Your developer can end up easily work in single corner, with few happy paths. Where as QA should touch nearly all surfaces of product. And even have idea what are most of the specs.
Exactly, we had 1 to 2 QA people compared to 6 to 8 developers, roughly speaking the developers knew more about particular details of like a third of the system where QA knew all the interactions.
That's definitely a fair point. However, that knowledge should live with other members of the team and it can be helpful for QA to have less knowledge of the system. How can that be helpful ? -- so they can view the systems through the lense of a typical end user.