Yes I agree to you. There is no way that Switchs sales of 2020 can be topped next year. Switch will end up at something between 6.0 and 6.5 Mio. units ytd at the end of 2020 and this will definetly NOT be topped in 2020. But I think maybe its sales will come close to this. By launching some big flagship titles like MH Rise, BotW2, Mario 3D World Deluxe, new Pokemon Games and maybe new casualstuff + new revision + bundles or price cuts, Switch should also have some great sales in 2021.
It will get close, but it also has the potential to beat 2020 with the right stuff coming out. I can think only of a few games that will have that kind of power:
Monster Hunter
A new Dragon Quest (or a remake)
A new Final Fantasy (very unlikely)
A new Pokémon
Mario Kart (perhaps?)
Mario
Splatoon (unlikely)
Not a game, but a revision will help a lot combined with any of the above games as a launch game.
Monster Hunter Rise is releasing soon, but I don't think that alone will give it the momentum throughout the entire year, the Switch needs a killer year (meaning multiple of the above) if it wants to beat 2020 sales numbers.
Unless NSW does 6.5mil++ then I still am a believer of NSW being flat or slightly up YoY. ;)
I want to believe as well, but without a revision or another "Animal Crossing" bump in sales, I really doubt it. I think the Switch needs perhaps 3 or so of the games I mentioned above to have a chance of another record-breaking year or a hardware revision combined with any killer game.