People expecting Switch to not affect PS5 and Scarlett are going to be in for a shock once they release. These consoles do, in fact, compete with each other. Sony and Microsoft are going to launch expensive consoles against Nintendo's cheap and popular console. How will they fare? What does history tell us?
For 2006-2009, the Wii was selling at record levels. At the same time the PS3, in particular, was suffering compared to earlier Sony consoles. This was not a coincidence. Wii was eating its lunch. People bought the cheap and novel console over the expensive and powerful one.
After 2009, we got a different story. Wii sales dropped off quickly, while PS3 and XBox360 sales were picking up. Again, this is not a coincidence. These consoles are competing. Sales of one goes down while the others go up. They are clearly competing with one another.
In the end, total sales for Sony/Microsoft for gen 7 were 87.4m (PS3) + 85.8m (XB360) = 173.2m. Meanwhile, in generation 6 total sales were 157.7m (PS2) + 24.7m (XBox) = 182.4m. There were about 9m people who switched to the Wii in generation 7, and had a Wii only. That means the vast majority of Wii owners (101.6m) decided to get a second console. For many households what happened was they bought a Wii first and then got a PS3 or XBox360 after the consoles dropped in price. Lots of gamers get tired of a console after 3-6 years, and good games on the Wii dried up after a few years. These Wii owners switched over to the PS3 or XB0x360.
That is the sort thing we should expect for PS5 and Scarlett. Again we have expensive and powerful consoles competing against a cheap and novel one. We should expect their sales to stall for the first few years. Most people are just going to buy a Switch instead of a $500 console. After that it kind of depends on how popular the Switch's successor is. People might transition from Switch to "Switch 2" or they might transition from Switch to PS5 and Scarlett.
Either way, all of these consoles are, in fact, competing with one another. Since Switch is such a popular (and cheap) console, expect it to take sales from PS5 and Scarlett. Anyone who expects these consoles to sell well right from the start is in for a big surprise.