You're making a huge stretch by saying "Mario related". Don't play naive. Yoshi and Luigi's Mansion are basically their own franchises. A port to try to put steam in a dying system hardly counts, especially when it's the last release for Nintendo's old 2-console model.
They're still Mario characters, they're still set in the Mario universe. They're still tied to the Mario brand. So both Yoshi and Luigi's Mansion still count.
|I'm not saying we can't have multiple Mario games per year, there's actually consistently been two Mario branded games a year for Switch since 2017. I'm also not saying it's never happened. I'm just saying 3 brand new Mario-centric titles in a single year for a single system is probably a bit much honestly, especially because Nintendo more so than with their home consoles are going to have to figure out how to stretch Switch's appeal for as long as possible. At that point just extend some of that Mario appeal to another year or something. This is all on one console, not two.
Even still, Nintendo will want to make sure there's enough Mario-related content on the system every year, especially to help keep software and hardware sales up. Like it or not, Mario as a brand sells, so there should be a good 3-4 games staring a Mario-themed games each year, in addition to other non-Mario stuff as well. There is such a thing as too much I agree, but nobody will complain about a handful of Mario Character games every year, especially if the games are at least decent.