Well I haven't played yet either and think you pose some very good questions and points. Trying to work within the limits of six sided dice seems to be a pretty serious constraint and then trying to keep it a "roll low" game as well.
Giving the Art a naval attack value seems odd to me too. Perhaps I'm misunderstanding but I don't know that there is a field piece that can dent any ship.
My impression has always been that you need some pretty serious emplacements to attack ships from land (at least metal ones.) Maybe I'm too "Guns of Navorone" and thinking too much of the bunkers in Normandy about it.
Maybe one of our more dedicated historians could help us out.
I don't know that the land value is too low but then I don't know how dug in units managed to get. Also if the land value is low because the pieces were small that also lends more weight that the Naval value is off. Do the ART give a bonus to INF?
I'm a bit skeptical of this game after seeing the combat system. I'm wondering if they didn't try to compromise to much between tactical and strategic and will fail at both. I didn't find the BOTB system confusing at all and when this 'Dreamblade' guy characterized it as such my doubts really went up. I guess BOTB went to far away from traditional A&A. I do find myself saying "Forget the other A&A combat systems when you play BOTB" often.
I will reserve judgment till I get my set and a chance to play.