I was right when I said the wii was going to sell way more than gamecube and I was right when I said the switch would sell way more than the wiiU. I was right when I said the ps4 would sell way more than Xbox one and I was right when I said the new consoles would come end of 2020 when everyone was saying 2019 a few years back.
If you get your predictions from hardware by date, then the wii would have sold minimum 150 million by now as it was a phenomenon.
If you use the same tool and match sales ps4 vs switch, you'd know they sold about the same for the first years, so the switch could outsell the ps4 in the end when ps4 goes out of production, lets say in 8-9 years.
Then again, I don't need tools, I have a brain, look at 3ds, it was outselling the ps3 for quite a while, still haven't out sold it to this date.
Switch can be scalable, but next gen games will be far too advanced to scale it to a tablet device. From next year the only AAA 3rd party will be remasters or current gen ports or low budget games.
Same with 3DS, there were newer games that couldn't run on the older 3ds (xenoblades for example even tough it was much worse than the wii version), so many of those 3ds sales were not new consumers, but people just upgrading.
In 2019 Nintendo sold really well due mostly to the LITE switch, which sold to people who only wanted a portable, but now there's not much reason to buy it, most people who wanted a hydrid or portable already bought it.
If they come out with an upgraded switch (lets call it a + version) most buyers would be people who already have a switch.
To put things into perspective, lets look at the numbers of software sold in total, probably things would look very different, I believe ps consumers buy more games than Nintendo consumers.
I have all consoles, but I do have more games on wiiU than switch, if we really think about it the switch didn't get many exclusives in 3 years, Xenoblades 2, Mario galaxy, Mario + rabbids and Luigi mansion 3, I never liked smash bros, I don't do fighting games and I don't like splatoon, I do not play online ever So what else is there on the switch? Most of third party games I'd rather play in 4K on my 100inch projector with much better graphics and performance at much cheaper prices, example witcher 3, looks horrible on the switch, performs worse, and costs 3x the price.