I think you are over simplifying. If it was a range toy the secret service wouldn’t use it.
The idea that a firearm is good just because a certain agency uses it is a fallacy. The Secret Service uses the P90 because it is high capacity, has a high rate of fire, and is significantly easier to conceal than a short barreled M4. The Secret Service doesn’t mind the fact that PDW calibers such as 4.6x30 and 5.7x28 require more shots than a 9mm, .40 caliber, 10mm, or .45 carbine, let alone a 5.56 because the advantages of the high capacity and ease of concealability are a high enough advantage for them to be fit in service for their extremely specialized tasks. The Secret Service has a very different criteria for firearms than conventional law enforcement, military, and civilian shooters.