You don’t send US Marines to a battlefield just to shoot the artillery. For one thing, the Army has better artillery (the Marines have nothing even close to the range and precision of the M270 MLRS), and more of it.
You send the Marines either because you want to show the colors or because you’re expecting their mission to evolve into something less long-range and more intimate. Or both.
Next stop: Fix bayonets, Devil-Dogs!
The Marines did the same mission at Mosul until relieved by the Army. I believe their expeditionary capabilities play well to this type of mission.
By the way, the Marines have HIMARS and the US Army has the same M777. Same capabilities. Granted the Army has more of each. That’s why they can both provide precision fires.