Is there anything in canon stating that The Federation only has one service - Starfleet ? Could they not have a military/peacekeeping force that absorbed the marines ?
Just because we only saw Starfleet personnel acting in The Dominion War doesn't necessarily mean there aren't any...does it ?
I assume planets would have their own forces, unless membership requires you to disarm them.
Still the above is why I support the idea the Macos were folded into security personnel. The supposition there's Marines leads to more suppositions which leads to more suppositions all to support the central premise. Oddly, the central premise isn't wrong IMHO, I just think the Security Personnel *ARE* marines. Just renamed
marines who also handle MP work.
As for Colonel West, he could have been part of Earth Security or have an honorary title from his home planet.