The handheld gaming market is not static and can also decline so Nintendo can also flop the same way PSP went from 80m to the vita's 15m, or DSs 150 to 3DSs 80m

Well, static enough to beat the 3DS lifetime sales within 4 years.

We're discussing the future. Between 90s/2000s/2010s there were drastically different sales of CDs. In 2008, someone would have said digital is taking over but the physical market is "static enough" to still represent the majority of sales, another 10 years later and physical sales are in the minority behind digital and streaming. 

Lack of competition + Exclusives + Japan will make whatever Nintendo releases as handheld to sell 20 to 30 million as long Nintendi give support to the system, if they drop it fast it will obviously tank just as fast

Home console market is much more competitive, so they need something to attract customers, Nintendo fandom alone can barely bring in 10 million sales as show by Wii U

Remember the Wii / Wii U change?

No Nintendo has already had 3 consoles not live up to expectations. They’re great when they create something that’s a gimmick like the wii and switch but have failed with n64, GameCube and Wii U

Keep in mind that while Nintendo has bombed their home consoles in the past, their track record with handhelds have been A LOT better. The closest Nintendo came to failing with a handheld was the 3DS, but that was mainly due to poor initial pricing. The 3DS was actually a very well-performing handheld overall given the stiff competition it had at the time from the smartphone gaming craze, and the hype from that has largely dissipated now in 2020. If Nintendo's only competition is the open market for gaming, Nintendo can easily win because it offers strict quality control that attracts gamers who get turned off by scams and microtransaction (this is true today as much as it was in the 80's).

The big issue I could see for Nintendo in the near future would be if Sony releases a competing crossover platform. Sony has been Nintendo's biggest thorn since the 90's and is the only company that seems able to really whip Nintendo at its own game in certain circumstances. I think after the Vita, though, Sony is probably content with not competing against Nintendo in the handheld market for a while.

I would say that it's Nintendo's to lose for the next generation and a half, after that who knows.

Historically they have to reinvent the wheel to make a hit. Wii was the winner because motion controls were new to console gaming. WiiU flopped hard due to banking on the existing tablet tech fad, which was beginning to fade. Switch used their handheld brand power which is unmatched and funnelled that into the console space. Genius.

I think as long as their dedicated handhelds are dead, their consoles can bank off their console/portable fanbase at the same time no matter what they do so long as compact portability remains a key feature.

yes.... unless they name it Nintendo Switch U