Getting parts and systems "space qualified" is a long and arduous process. The stations on the ground for communication and launch are also quite different from other Air Force operations. The real mission of the Space Force is to separate out the development and logistics so that both can run on their own individual tracks in a more streamlined process.

It may sound trivial, but logistics is absolutely critical to the modern military. If you don't have bullets, you can't fight. If the space division is taking time and attention away from the atmospheric-based Air Force, which should be focusing on various forms of bombing and air superiority, then you slow down both divisions.