I think dynamic entries should be used on hostage situations ONLY.
They are so overused these days.
By making it a state unit, the local police wanting a SWAT raid would not only need a warrant, but also have their warrant and reasons be convincing to the SWAT commander who is not under their chain of command, and who does NOT want to be associated with a major screwup in judgement.
By making SWAT consist of a few units in the state, it would be possible to have SWAT be better trained and equipped, and also faster to deploy, since it would become cost-justifiable to give them helicopter transport.