It didn't use to be. But as soon as they started launching national security payloads on the Falcon Heavy and the Delta IV Heavy retired, they became the only h

It didn't use to be. But as soon as they started launching national security payloads on the Falcon Heavy and the Delta IV Heavy retired, they became the only heavy-lift launch vehicle on the market capable of taking up national security payloads. Until Vulcan/Centaur enters the game.