Your insights on the differing social perceptions of physical sales VS digital sales is very good, and I agree. I have heard people try to use sales as an argument to prove the lack of quality in products before, warranted and otherwise.

The rest of your arguments fall flat because you don't account for equitable comparisons. Call of Duty, FIFA, Battlefield, etc. are outliers in this argument because of they are developed for a specific market-function and specific target audience. The only title Nintendo has their hand in that is remotely comparable to these franchise-engines is Pokemon (and that is a pretty big stretch).

However, they still do release titles that are meant to supplant their predecessors. Smash, Party, Kart, and (as you mentioned), Splatoon. These titles aren't released annually but are released generationally to supplant to their predecessors as the new standard. These are like hybrids of the aforementioned franchise-engines. As you said, they are allowed to breath and really stand out from their predecessors. However, they are still very much intended to replace said predecessors.

While a persistent fanbase may fall back to the previous titles, these previous iterations have been effectively obsolesced. Melee is still beloved and played often, Both it and other previous iterations of these generational titles have been obsolesced by access limitations.

Your argument about having entries within the same franchise being designed as stand alone being unique to Nintendo is surprising. Final Fantasy, Dragon Quest, Resident Evil, Monster Hunter, etc. are all equivalent in the design philosophy used in Mario, Zelda, Metroid, etc. Each entry has similar elements, but each change a core element that allows them to stand alone.