And if you want to ignore the context behind those "2 in 3", so be it.

2016

PS4: 17 590 483
XB1: 8 368 621

2017

PS4: 20 144 528
XB1: 7 647 153

This is what irrelvant means.
The most popular console, not only was untouched, it grew despite the 13 097 768 Switchs sold that year.

The only revelant difference between Switch and the others, is portability. But if you look only at that - and you probably will - you'll forget that it came packed with system sellers (two special ones at that) and the fact that by that time, PS4 and XB1 already had 80+Million consoles sold combined.

What those numbers show is that Switch is making it's potential market out of those 80+Million sold. With only 30% of it's sales coming from outside that ecosystem. That's not a healthy situation.
What should be happening is the exact opposite.

Who cares? Well, Nintendo does.
Do you think any company wants to be a complementary thought? That means there's a real danger that when things change (moving on to a new generation, for example), the secondary console may or not be bought. Whereas the primary console is THE priority.

I relly dont understand whats actualy your point, clear fact that 70% of PS4/XB1 owners also bought Switch means that Switch is different enough compare to PS4/XB1 and that you are wrong when said "They are not "different enough". PS3/XB360 and Wii were". I cant believe you trying to argument against clear numbers and facts.

What you posted proves that Switch of irelevent to PS4/XB1 sales/succes same like XB1/PS4 are irrelevant to Switch sales and succes because they are different enough.

Switch has very strong and healthy sales, I can belive you can't spin that in any case.

Nintendo dont care if Switch is selling like primary or secondary console, they care just if is selling. But even with other PS5/XB2 Switch will be good secondary console, Switch will still be different like its different currently. Also Switch is curently bought by plenty of PS4/XB1 owners like secondary console, but how time passing more people will buying it like primary console.

In what regard is Switch different? Portability? 'Cause that's the only "major" difference.
And if you only look at that you are ignoring the rest that makes Switch a worthwhile purchase. 
So, what do you believe that makes Switch different?

Those 70% bought a Switch because they didn't have to choose between a PS4/XB1 and Switch. If they had to choose, seeing as only 30% don't own another console, Switch's sales won't be as high as they are.
Second. PS4 and XB1 have enough time on the market for their owners to be satisfied and open to something new. Switch was that something new. Hence, most Switch owners already had a PS4 and/or XB1.

Sales of XB1 and PS4 didn't go down - or down enough, in XB1's case (by the way, XB1 is having it's best year in 2018) - because the majority of it's users didn't have to opt between a Switch and another console: there already was enough of them with a PS4 and XB1.
And that is why i said that Switch is living off of their already established market. With only 30% of Switch's sales coming from new users.

 "Switch has very strong and healthy sales, I can belive you can't spin that in any case"
And again, i can't believe you are making this a topic of discussion.
I never said Switch sales aren't great, nor even hinted at that. 

What i'm doing is trying to analyse how these same sales came to be to understand what this represents for Switch itself and for the next console.
So far, the conclusion that we can make from that data is this: Switch is not seen as a priority and when the time comes, assuming that doesn't change, when it faces real competition and has to fight for new users, those 30% don't make for a bright future.

"Nintendo dont care if Switch is selling like primary or secondary console, they care just if is selling. "
No. You don't care.
Nintendo understands very well who is buying their console and what that means for the future of it's console and even next gen.
If you actually believe that Nintendo ignores this, then, i'm sorry, you don't understand how a company of this magnitude operates.

"Also Switch is curently bought by plenty of PS4/XB1 owners like secondary console, but how time passing more people will buying it like primary console."
And why do you say this?
A hot new hybrid console, coupled with Zelda, Mario, MK8, Splatoon 2 couldn't get more than 30% (new) users, what makes you think that goal will be achieved?
All these things will not hold the same value they have today and i'm not seeing Nintendo have a better year in Switch's life.