Exactly. I cannot agree that Porky, Black Shadow, Medusa, Hades, and Wart are "iconic".
While Porky is a major villain in the EarthBound series, the EarthBound series itself isn't a major Nintendo franchise. There are only three games in the series and the last game came out in 2006.
While Black Shadow may be one of the major villains in the F-Zero series, the F-Zero series itself isn't a major Nintendo franchise. There are like, what, 5 or 6 games in the series and the last game came out in 2004.
Medusa and Hades may be major villains in the Kid Icarus series, the Kid Icarus series itself isn't a major Nintendo franchise. There are only three games in the series and the last game came out in 2012 and before that, in 1991 in the West and 1986 in Japan.
Wart is not a major villain in the Mario series. He is not a recurring Mario character. He is best known for being the villain of Super Mario Bros. 2 and that's his only contribution to the Mario series. Even a mini-boss (Birdo) from the same game is a recurring mini-boss in RPG games and a recurring playable character in spin-off games.
I feel that the only notable Nintendo villains left are Kamek, Birdo, Skull Kid, Ganon, and even the Team Rocket trio (Nintendo acknowledged that the most famous members of Team Rocket are Jessie, James, and Meowth).
Kamek and Birdo are from the Mario series, a major Nintendo franchise. Skull Kid and Ganon are from the Zelda franchise, another major Nintendo franchise. Team Rocket are from the Pokémon series, obviously a major Nintendo franchise.