Personally I’ve always thought of the Alter cup as the Nationals for Portsmouth sailors.
Key West serves as a Big boat Handicap Nationals and it succeeds because there are a huge number of monohulls who race PHRF and their owners choose to not conform to a OD standard. They travel to Key west for national competition in the rating bands that the chief handicapper sets up.
Nationwide, we don't have enough dead boat society racing boats to make a Portsmouth class. For instance in the Chesapeake, we have a SC22, a H20(DBS on the east coast) a N6.0. These boats have not made a weekend race this season and passed on last seasons big "run what you brung Handicap race aka the Pumpkin Patch which is also scored for One design classes.
The Alter qualifiers could not survive on Portsmouth only sailors. It is built on One design racers competing on Portsmouth.
I think the vast majority of one-design sailors (mono and multi) have much more of a stake in their own class championship than any of the US Sailing championships.
No doubt! the question is... Is there enough oxygen, time, money, and sailors for both kinds of events.