Which is the best way to de-grit clams and mussels? Salt, cornmeal, or salt + cornmeal?
I think salty water is a given in purging, and the article you shared is no exception to this. Quoting directly

You need lots of water—about 1 gallon of water and 1/3 cup of kosher salt per 1 dozen clams—that should be changed several times over 48 hours in order for them to be squeaky clean

I think salt and cornmeal can be used complementarily. As it’s mentioned in the article cornmeal will alter the taste, but it will also expedite the purging (from 48h to 24h per the experiment in the article).
It looks like using both is a better option than just using salt. And assuming salt should always be present in the water, I would rule out the only cornmeal option.