The Air Force does launching and flying over land as well as land based missiles. Flying over water is the navy’s business.

This. All services have experience doing most things - they do those things to maintain superiority over their domain. And the way they do them is specialized to that domain.

The navy was up there to maintain superiority over water. The airforce over the air. The army likewise.

But nobody clearly owned maintaining superiority over the domain of space and any operation that needed to ensure uncontested operation in space was a joint agency nightmare.

Space force is chartered to provide superiority in space so the other services can conduct their operations up there. Space is clearly a specialization that is differentiated from the air.

I've known Navy people to make the case that the Air Force shouldn't be separate from the Navy. I have no idea if they're right, but I'm sure there are websites arguing the pros and cons out there.