Nope, it isn't. If a competitor entering the market doesn't shift your sales (and PS4 had it's best year when Switch launched, and this year is like 2nd or 3rd best with the decline being natural for the age of the console and hitting peak last year) then it isn't a direct competitor.
If Xbox wasn't on the market (mainly USA and UK) PS4 sales would have been considerably higher.
Come next gen and if Switch 2 eat away market from PS5 or X4 then you can claim this.
I think you're wrong and confusing others on purpose. The Switch, the Xbox, the PS4, are all competitors. Why? Because they all compete for a consumers time and shelf space. You can't deny that fact. Two or three competing devices in the same market not eating each others sales is a dumb analogy since, like in every other market, you don't know what decisions consumers make except for the actual hard raw data that we get. We cannot determine that for example that a consumer chose Smash Bros over GoW this christmas. You can't write that as a loss of sale for GoW, because extra piece of motivation is missing. What we do know however is that these platforms wrestle for time and attention, by software releases (sometimes exclusives, or superior plats) and other measures. If they didn't compete directly, we would not see this. And it is so very obvious that they do, you have to be living under a rock to not notice it. If you do know it and still deny this simple fact, you are being malicious because A: You don't like the fact that the Switch is doing well against your favourite platform and B: A platform you like is losing market dominance slowly.
As for the next Xbox or PS5, I am not worried at all for the Switch. This year will be notable because of certain releases the Switch will get, at which point it will become a platform with a library difficult to ignore. By then, a strong exclusive lineup will push it forward. A new powerful platform doesn't always win over a weaker platform. It always comes back to the games.