Now who's being silly? In the case of the Xbox One, that weaknesses is far more pronounced in the wider markets, the U.S isn't quite as lopsided. The gap between them, this month in particular, isn't so large that they 'aren't competition,' not by a long shot, and it combined with the Wii U actually take more than half of the total current gen console sales this month. (Again, in the U.S.) you are literally claiming that without those two consoles, that extra 230k sales would, what, vanish into the ether? That not even a quarter of those who bought an Xbox One or a Wii U this month would, with no Wii U or Xbox One to choose, opt for a PS4 rather than buying nothing at all? Care to explain why?
The claim that having two competitors make the PS4's situation no different then the PS2's when it had, literally, zero equivalent generation competition that summer, is ridiculous and just lazy thinking.
Yes the Xbox One isn't quite just quite as weak in the US but but does that matter that much since there were some cases where the PS4 nearly doubled/doubled on the Xbox One in some months ?
Why would Nintendo gamers be interested in a PS4 ? It's clear that almost none of them are interested in a lot of Sony's first party games nor are they interested in third party games so it's most likely that they would just quit gaming altogether.
With the xbox one it isn't clear what things will happen. If they do continue making games they'll be releasing them on PC from now on which would mean that Halo as well as other Microsoft titles will be released on there. If that happens a fair portion of xbox gamers will be migrating to PC or will be returning to PC gaming because of this. There's also small portion of Xbox gamers who are also disinterested with a lot of playstation exclusives so I can see them also going to PC rather than continuing their habits on playstation plus I also happen to share their sentiment about PS exclusives too.
Causation does not imply correlation. Not everyone will opt out to buy the PS4 if nothing else exists.