>Geno, a niche character who appeared in one game 20 years ago
>Erdrick, the Marth of one of, if not the most popular video game series in Japan and overall one of the largest video game series not represented in Smash
People at least know Dragon Quest in passing; Geno is a literal who outside of the Smash fanbase. It comes down to the core vs. the wider fanbase, and I can't imagine Nintendo catering exclusively or majorly to the core fanbase, as proven Isabelle, Incineroar, and Piranha Plant, none of which cater to the core fanbase. The Nintendo Promotional Rep was a bone thrown to Nintendo because its realistic.
K. Rool is an exception because EVERYONE wanted him. America, Japan, Europe, the core fanbase (who brigaded the Ballot), old time fans of Donkey Kong Country, etc. If you participated in any sort of Smash Bros. speculation you would know who K. Rool is, or if you watched any Top 10 lists K. Rool was 10/10 times going to be on that list.
The major Smash poll on Reddit proves that most of Geno's fanbase comes from America, and therefore he has less popularity in other countries. I'll concede that he is popular, but he is certainly no King K. Rool.