And while Hoshi wasn't promoted, neither was any other ENT cast member. Even T'Pol was commissioned at equivalent rank. Since Starfleet in that era seemed to be going by the old Royal Navy traditions, with no "half-pip" ranks, it's possible that promotions were less common.
If the holoprogram is taken at face value, we don’t know enough. They could all been promoted in that timeframe and earned an extra pip or two, and been assigned as first officers or captains on other ships elsewhere during the Romulan war, and then took a temporary demotion in rank weeks before the founding of the Federation upon returning to Enterprise. And the holodeck historical logs made an error in literally demoting the crew when creating the program. A not implausible theory as Archer never had more that two ranked commanders at a time, and having four first officers on the bridge, or three captains on a ship that been decommissioned would be weird. Not to mention that Archer, while never promoting anyone, never demoted anybody either even when he should have (see Trip in “Cogenitor”) or even suggested that it would impact his career or Trip should resign his commission over it.
All we know is that within four years of the Federation’s founding, Hoshi retired at the rank at Lieutenant Commander, indicating that half pips have existed since the beginning of the Federation.
And before the NX-01 was launched, Archer was ranked commander and Trip a lieutenant a decade prior in the NX Project. So it was not like United Earth Starfleet had a problem with promotions in general.
Hoshi is a more complex case as honestly she was done far more "dirty" with her being an ENS in the first place, but IMO if you accept that and that she had no change in position (bear in mind, unlike Kim JG doesn't appear to be available), then her not being promoted makes sense.
Also remember that Hoshi got expelled from STC. And was only brought on because Archer needed a linguist and was friends with him.
Maybe the ensign rank in the ENT era was meant to cover brevet ensign ranks as much as it covered for the rank of lieutenant commander.
Aside from Janeway, who couldn't go above captain for obvious reasons, every other ranked character got either a promotion or a commission.
Chakotay - Commission reactivated at previous rank of LCDR.
Tuvok - Promoted from LT to LCDR.
B'Elanna - Promoted to LTJG and chief engineer... for hitting a superior.
Tom - Commission reactivated at LTJG. Reduced to ENS, promoted back to LTJG.
Harry - Never promoted.
EMH, Neelix, Kes, Seven - No rank.
Chakotay, B’Elanna, and Tom were a part of the Maquis, while Tuvok went undercover to spy on the Maquis.
Two things can bee gained from these observations.
Maybe Harry should have shown some signs of being a Maquis rebel, or be willing to go undercover and act like one of them?
Seems like Janeway had more sympathy for those that had anything to do with the Maquis, and was protecting them from prosecution from Starfleet before they arrived home. While Harry did not need protecting since he was squeaky clean.
