I kinda agree with some of your points but disagree with the others:
First of all, WiiU is not really a valid comparison as it sold way worse than Xbox One currently is. Xbox One will end up outselling WiiU 4:1 or even 5:1. So, it is definitely not the kind of disaster WiiU was for Nintendo.
Second - actually it already happened and there is nothing MS can do actually. There is no way for them to sell as much as their competition sells. My original post was dedicated to their decline that we see here. XB1 seems to end this year even worse than the last. And the last year was already pretty bad. That's the real problem here. Not that they can't reach PS/Switch numbers as it is already impossible at this point in the gen.
I do agree with you though that it is not something that should be considered as a norm in general. They lost the gen because of their own huge mistakes in 2013.So, this is what they get for it. Better luck next gen maybe.
Yeah, you're right but there isn't a fair 1:1 comparison with a Nintendo or Playstation console, because Nintendo consoles sells too well or too bad and PS have not bad selling console yet (at least home console).
And with your second, I agree again. Xbox One will never be able to reach 15-20M a year, but when people say, that XBO in 2018, did "phenomally", to me that's a lie, and it's unfair to the others. if XBO this year, thanks to X and Game Pass reached, for example 10M sales, i would be the first to say that XBO in 2018 did "good". It showed progress. But if in 2018 you're only reaching the levels you had before last year that was you worst year ever...., that's not good at all.