That doesn't explain why it would lack dry fording ability or didn't have an easily accessible loading area.
Well most gunwagons nowadays are not amphibious or indeed sealed and can ford usually around the 500mm-750mm mark which is enough for most streams and low water courses.
If you're fording a river/water obstacle deeper then that then you might use something else or daisy chain vehicles like we do now.
We also sling kit on the outside of vehicles and the Argo buggy is fairly small to have much in th way of load carry capacity. The Argo looks to me more like a SEAL DPV etc.
Light, fast only used for a few Days recce/strike missions at most and you'd just sling kit onto it.
It's a very specialist type of vehicle.
My thinking is in ST it was designed for use on planest where shuttles/transporters are unreliable due to weather, geography, enemy actions (jammers ect).
Instead of having to be dropped off and walk you get a light strike buggy.
If it get's wasted, no big deal. You can pretty much replicate them as needed.
On the other hand, TAS style forcefields would be "barebones" technology by Trek standards, probably much more reliable than crankshafts or spring suspension. So the weatherproofing, dustproofing and fording issues might be solved by assuming such a field. Only the awkwardness of Worf's position might need critique, then.
We never really saw much in the way of defensive shielding in ground combat anyway....plot devices I guess.
I could also see Starfleet having nothing to do with the Argo, of course. It might be Picard's very own hobby project, about as practicable for mobility as the horses or sailing ships that Picard loves to operate on the holodeck. For all we know, it is an exact replica of a 200-year-old design that pleases Picard's eye and offers a sufficient challenge to his driving skills, buttocks durability and so forth. The one really odd thing about that would then be Worf's cannon.