Historically my nintendo x 3rd party ratio is about 70-30, switch is a bit different however because Im buying more games these days and nintendo games are finite. Nintendo has built a real trust with me, Im happy to pay $80 on a whim if its a nintendo handled game because I know it will be a quality product and most importantly; enjoyable. I get burnt time and time again by 3rd party devs due to things like: incomplete testing, a difference in mainstream/personal taste, lazy developing, industry trends (clones) and as a Nintendo gamer, shit ports with no soul and lacking basic features. That said, there are so many 3rd party gems these days but nintendo is just the safer bet for me.
With Nintendo games we're at least guaranteed a certain level of polish and stability, as opposed to third party games where we run the risk of serious bugs, poor performance, only half the game or less even being on the cart, etc.
Nintendo makes a lot of good games. That is why most people purchase Nintendo Systems. Its not for their Third Party games. That being said I am not buying New Super Mario Bros U even though I didn't own Wii U.
You're not missing anything worthwhile, NSMBU is the definition of bland mediocrity, it's not worth buying.
Bet with Liquidlaser: I say PS5 and Xbox Series will sell more than 56 million combined by the end of 2023.