Not the point I was making. You still get subject specialists at Primary school, I.e maths & science graduates.All primary teachers are able to teach maths and science in state schools. In London it isn’t easy to recruit for a class teacher, but you can do it, and you can be selective I think. Retention is quite another matter, as is management roles.
My wife’s a primary head teacher so I am aware of the issues.
You actually need to recruit good teachers rather than just people who know a subject; this is an unintended consequence of golden hellos for certain subjects.