I don't think many of the ARC boats are in the smaller size range. All it takes is a few 50+ footers with large tankage to push the average up quite a bit as well.
Adding tankage is not that difficult. Buy the boat you want for reasons other than tank size and add capacity later.
Agree with all.
Note also that many boats have factory option tankage that will equal your desired gallonage, like many Ericson's in the 32 to 35 foot range -- many of those had three tanks.
My Olson came with two factory tanks holding 46 gallons total, and I replaced one with a larger tank to bring our total up to 61. With our ability to use either tank via a manifold, we add water for whatever duration we need before planning a future marina visit. With more than one tank you can add or subtract to better balance the boat for performance, too.