More like Johnny-come-latelies: Archer already had people toting plasma and phaser rifles for a living and keeping the ship internally secure (with about as much success as the MACO later had)...Besides, the way ENT treated the MACOs in season 4 seemed to suggest that they were intended to be the forerunners of Starfleet Security.
Since there was a Starfleet, one would assume there to be a Starfleet Security already as well. The tasks would exist with the existence of starships, so why not the organization and the personnel, too?
Or with the name of Cornell West... In any case, him being associated with ground forces is somewhat ill-founded speculation. He presents a plan of using starships to liberate Kirk and McCoy, after all!Except that he wore a Starfleet uniform with a vice admiral's rank pin, which would correspond to a lieutenant general. Memory Alpha speculates that he may have been a Starfleet vice admiral with the billet (job title) of colonel.
Interestingly, when we do see ground fighters in DS9, their rank titles appear naval. That is, we don't get "sergeants", and when we do get ground-fighting "captains", they are the superiors of "commanders", not the underlings of "majors". With "lieutenants", we of course cannot tell much.
Timo Saloniemi