It would have been so much better had Earth sent a battle group.
How do you send a battle group if you only have one ship? That was more or less the whole point of the entire show.
On the issue of how "military" the UESF was, the only time its supposed "nonmilitariness" is brought up is when Archer and Forrest discuss bringing the MACO team aboard. In that scene, the MACO are the military, and the UESF is something else. It looks, sounds and quacks like interservices rivalry more than anything else. That is, the MACO are the army (or what was called "the military" in English until very recently), while the UESF is the navy (which was very definitely not a "military" in English just a few centuries ago, and you'd have gotten yourself keelhauled if you claimed otherwise).
The same could apply to our sole TNG piece of "Starfleet is not military", from "Peak Performance". Picard there could be arguing that since Starfleet is the navy and not the army, Starfleet doesn't do mindless drills such as the one he is now ordered to conduct. Starfleet has better things to do in peacetime, just like any old-time navy would, while the army just sits in its garrisons (or doesn't necessarily even exist) unless there's a war.
Clearly people wearing Archer's kind of uniform are supposed to be Earth's leading space combat experts. It may happen that Archer himself is not a particularly good expert in that field, of course: being Henry Archer's son may have counted for more in the original selection process. But replacing Archer with, say, Hernandez or Ramirez would be a bad move when Archer is the only military skipper with two years of real deep space experience.
Archer himself never shies away from considering himself a soldier. He just happens to be an explorer as well, much like ol' Cousteau. Picard doesn't go out and say "I'm not a soldier", either; he just at one point argues that UFP Starfleet isn't a military organization, whatever he means with that.
If they left Earth for the Expanse with still 80 people aboard, that means that up to one quarter of the original crew were replaced with the detachment of MACO's.
And that's the point; the original crew featured a bunch of scientists and whatnot, the combat mission crew featured the like number of Marines, and neither configuration suggested there was any excess fat as regards space combat capabilities. 3/4 of the crew was always considered essential for that, and then there was 1/4 more for the groud combat side show.
We thus lack any and all evidence that the ship would have "excess" that could be trimmed down. If we had witnessed an initial exploration crew of 160 being trimmed down to a Xindi-hunt crew of 80, we'd be aware of 50% excess. But this did not happen.
Granted, Archer might have
wanted to sail out with an exploration crew of 160, and was prevented from doing so because he never launched for an exploration mission, but only for a premature ferry mission where certain items and perhaps personnel had to be left behind. Perhaps the ship really is rated for 200 people, and a smaller one would do for the Romulan War. But we can't use ENT as evidence for such speculation, because the crew size stayed constant.
She wasn't sent because she was considered a "combat vessel."
True enough. But the only difference between her and the
Intrepid seemed to be the warp five engine. And the
Intrepid wasn't an exploration vessel, because NX-01 was supposed to be the first. So it would appear both the
Enterprise and the
Intrepid represent the UESF ideal for a space combat vessel... Whether that ideal would somehow change at the onset of the Romulan War is unknown, but again ENT doesn't suggest a reason as to why this would be.
Timo Saloniemi