...Nor do they have useful payload areas or practical means of loading or offloading, or ways to keep water out during fording or swimming, it seems.
Why not? It's not as if we should expect 24th century powerplants or motors to be so clumsy as to take up as much room as a diesel or gasoline engine and transmission today. A future windshield wouldn't get scraped and clogged by dust, either. And why doesn't the suspension work better in the future?
Okay, we can argue that the Argo has
a windshield and weather cover, but it is based on the technology of the TAS life support fields. Picard would obviously not deploy that, as he wants to feel the wind tugging on his ha... uh, face. Nor would he deploy it when the locals attack, because TAS fields don't stop weapons fire.
The other shortcomings remain inexplicable, though. Why isn't Worf's gun stabilized? Why is there no proper forcefield generator aboard, a perfectly regular shuttlecraft one, capable of stopping artillery shells and hand disruptors? I mean, if the vehicle were configured for "civilian" missions, the generator could well be omitted - but why would the gun be present in that case?
I don't want to evaluate the Argo as the cutting edge of Starfleet surface combat vehicle development, because obviously that's not what it is. I don't know what it is
for, but that's not a big problem. But even as a general all-terrain vehicle, it fails on practicability grounds, as it will be really wet while fording and is difficult to climb into, or to load.