Except that claim about Namor's supporting cast isn't true at all. Bob Harras, who followed John Byrne, used Namor's supporting cast extensively. Harras used Tiger Shark, Tamara, Lord Dara, Lord Seth, Vashti, Morel, Namorita, and Princess Fen.
Now, if he's talking about his surface world cast, perhaps, moreso, but even there, we have Jim Hammond, and Diane and Walter Newell. As for villains, Byrne even used Roxxon who the Atlanteans have encountered previously.
It's not that Namor doesn't have a supporting cast. It's that writers keep wanting to ignore the previous characters, so they can invent a new cast.
All that said, it seems Cronin is on a Namor kick. And I approve.
I remember that article too. Though it is probably packed away.