“didn’t want to sacrifice his men just to beat the Army into Baghdad”
That’s actually a fairly serious offense in the USMC. Kidding of course. But seriously, Marines are very light, so speed and violence are the key to success. That leads to lighter casualties by shortening the battle. While he dithers, the bad guys move other things to where you don’t want them.
I understand that was Patton's creed as well. There are many who see Patton in Mattis, and I think I agree with them.
My understanding was the entire campaign was designed to dislocate the Iraqi defense so that the Army could hit the Karbala-Gap with superior force. The Marines were on the flank, so it was always intended that the Army would kick in the front door — with tanks.