That is still ignoring a whole host of factors. For one, the late ports of mature games on Switch... all 5 of them so far, have generally been undermarketed, overpriced and launched with mediocre performance or other issues such as mandatory downloads (LA Noire, DOOM, Wolf 2) or game-breaking bugs (South Park). They also, apart from Skyrim (which, coincidentally, sold quite well on Switch), haven't been in terribly 'large' franchises, whereas many of the late ports of more casual games have massive names like Mario, Crash and Zelda behind them.
So, right now, we have three categories. Correct me if I'm wrong:
Mature late ports that sold decently-to-well on Switch:
- Skyrim
- Bayonetta 1+2
Mature late ports that sold 'OK' on Switch:
- DOOM
Mature late ports that sold poorly on Switch:
- South Park: TFBH
- Wolfenstein 2
- Payday 2 (?)
And then add in LA Noire, which I'm assuming sold OK, and the not-mature-but-still-not-like-Nintendo-games such as Fifa, NBA and WWE (which, again, I'm assuming sold OK, OK and Poorly respectively) and I don't really see enough evidence there to conclusively decide that Nintendo fans don't buy mature third party games. This is especially true when many of the games that sold poorly were either broken ports, overpriced ports, or both. Dark Souls could have been a good indicator of how well a third party mature game could do on Switch but, of course, that had to be delayed as well.