I think my comments were misinterpreted, combined with a overstatement on my part. However, I do believe that within the POTUS's direct control (i.e. can receive direct tasking from POTUS without Congressional or with limited Congressional oversight) there is not much else out there that can do the broad spectrum of operations that a MEU can do. Part of this has a lot to do with the Marine Corps USC Title 10 directed mission. Additionally, the MEU maintains a Direct Action capability with its Maritime Special Purpose Force assigned to the BLT. This is staffed by a combination of a specially trained rifle platoon, an amphibious recon platoon, and a force recon platoon.
But Foreign Policy is so much more than a summation of total combat power available to the CinC. A MEU has the ability to quickly respond to a wide variety of crises both kinetic and otherwise that can significantly shape another country's response to the US Government. With the sustainability it provides it can remain on station for a very significant amount of time without additional support. We do not require other agencies to establish an expeditionary airfield in order to flow logistics ashore.
I urge you to look at the following instances where the MEU or an element of a MAGTF played a role:
Battle of Najaf
Hurricane Katrina relief efforts
East Timor stabilization operations
400-mile amphibious assault over Pakistan into Afghanistan establishing Camp Rhino as the first major US FOB
Invasion of Iraq
Rescue of Jessica Lynch
HA/DR operations in Indonesia, Sumatra, and Sri Lanka
Battle of Ramadi
Battle of Haditha
Kosovo
HA/DR operations in India and Bangladesh
Counter piracy operations off the Horn of Africa
Haiti relief efforts
Lebanon NEO during the Israel-Lebanon War of 2006
Libya No/Fly zone enforcement
TRAP of the pilot of a downed F-15 in Libya
Battle of Fallujah (Operation Phantom Fury)
Operation Tomodachi
Reenactment of the Inchon Amphibious Assault with the RoKMC
Each one of these events produced a significant impact on the local populations where they were executed. And those actions absolutely effect the manner in which another sovereign power will choose to react/respond to the US Government. So no, I don't think it is that out of the question to see the MEU as playing a significant and rather sizable role as a tool of Foreign Policy available to the POTUS to accomplish both DOD and Dept of State tasks.