I have experienced the opposite. After the dedicated QA team was disbanded and repurposed to development, where every developer had to write tests for someone else's code, the code and designs started to become more testable, the tests eventually became simpler to maintain and understand. (the project was and embedded system)
The "We" and "Them" distinctions made people in different teams and different roles ignore the needs of the others. The change brought a culture change and also gave a view on the needs of the other side. This could make it possible that for the first time the development of tests and features could really be done in parallel (officially that was the methodology before, but never really worked out well, because the testability considerations were usually ignored at design time, and the docs were lagging, because of the bad bandwagoning culture. With the mixed team where everyone was treated as an equal these problems dissolved surprisingly quickly (in less than half a year)).
So my point is having dedicated testers can give base for bad culture which hurts the product and the company. Having everyone do the same job with regards to development and testing is better.
There is no silver bullet here. For some teams it makes sense to integrate development and testing. For some teams it makes sense to have dedicated QA people. For some teams a different constellation is optimal. I know developers that are brilliant at the big picture, finishing the implementation however was lacking. I also know developers that cannot get the major architecture right, but they can finish tasks and get it shipped. pick one of each and a devops guy that can write tests, and you have a team of 3 that produce top quality software.
You are probably right with your example for a small project. The one I referred was a medium sized safety critical piece with dev/test staff of hundreds. My example was for such larger organization.
Small teams almost always worked out well for me if a single leader person was present to sort out initial problems.
The "We" and "Them" distinctions made people in different teams and different roles ignore the needs of the others. The change brought a culture change and also gave a view on the needs of the other side. This could make it possible that for the first time the development of tests and features could really be done in parallel (officially that was the methodology before, but never really worked out well, because the testability considerations were usually ignored at design time, and the docs were lagging, because of the bad bandwagoning culture. With the mixed team where everyone was treated as an equal these problems dissolved surprisingly quickly (in less than half a year)).
So my point is having dedicated testers can give base for bad culture which hurts the product and the company. Having everyone do the same job with regards to development and testing is better.