I really don't see the issue with characters being "one-off". If Cloud had never appeared in another game after FF7, would anyone say he wasn't iconic/popular enough? What about Shovel Knight or Duck Hunt? If a one-off character is a great, iconic character then their number of appearances really shouldn't matter.
Super Mario RPG is one of the best SNES games and is usually on a lot of people's top-10 RPG of all-time lists, and it generally gets 9's across the board. The game added a lot of unique characters and locales that clearly have stuck with people because of how good they were. I used to watch my brother play it when I was like 4, and Mallow, Geno, the Axum Rangers, and Smithy all stuck with me far more than some reoccurring Nintendo characters (Bowser Jr., Little Mac, the whole FE crew are far less memorable and iconic for me).
Honestly, character wants are personal choices and are like opinions. Everyone has them, what's important is to respect those of others as long as it isn't Steve or the Dragonborn.