My personal take has always been that Starfleet is a USO (Unified Service Organization) basically taking all of the varies military organizations and blending them into one (mostly) seamless whole. Therefore there really are not MACO's or Marines, or Navy, nor Andorian Guard nor Vulcan Protectorate or Tellarite Fuzzy Wuzzies. There's just Starfleet which has elements of all of them.
Quite honestly I have never liked "Colonel West" and quite honestly given what we saw go on and what was invented in DS9, I personally just dismiss him as a Section 31 agent who they fed the President a line of bull about since I figure that your average civilian in the 23rd and a half century is as knowledgeable about Starfleet and its inner workings as most of us would be about today's military, plus I imagine that any government leader relies on experts to brief him and if you spend too much time doubting those same experts the job is going to get infinitely more difficult than it already is. In this case sadly President Ra Ghoretti got scammed.