Pokemon sales usually dies once a sequel is released. This time we don't have a third version cannibalizing the standard version, so I'm expecting similar legs to XY

However the 4.3 million sold in its second calendar year comfortably outsold XY second year (2.3 million), even though sales dropped over 40% Q1 2021 vs Q1 2020 it's easy to understand, Q1 2020 was the quarter after launch so sales were still high, I'm expecting a much more smoothy decrease YoY for the next quarters. We can expect at least 2 million copies for 2021 and 1.5 million for 2022. 25 million is the absolute minimum for this game

With Arceus predicted to come out early next year my bet is a next mainline Pokemon gen is coming only by 2023. This can be enough to give Sword-Shield additional legs to reach something in the 26 million range

So my prediction is 26-27 million

Answering the other question: I haven't bashed the game before its release because even though Dexit sucks it could be easily solved with future updates

I bashed the game AFTER it was release and I finally played. Could tolerated it like I did with XY (meh game, but nice competitive) and SM (a bit better than XY, but worse competitive)

But this time both single player and competitive  sucks. They fucked up with competitive with Gigantamax gimmicks. Overall not planning to get the next mainline Pokemon game. The fatigue just hit me hard. I'm willing to play their spin offs though, like Pokemon Snap

I get that, but don't you think the series could have evolved? Seeing how GTA went from strength to strength and ended up selling 100m+ copies, I really thought that Pokemon was capable of making that kind of jump. It is a series that can sell 40m+, and at twice the price of previous iterations. I think that would've complimented Pokemon Go and even pushed it further. But hey a man can dream 

Oh, absolutely, it could be great. They have the resources to do it, and they could take all the time in the world to add all of the mechanics and features that were abandoned, plus many more. But they wont, since Game Freak and The Pokemon Co. are too comfortable just how they are right now.

Below 22mil doesn't make any sense anymore, it's clearly going to outsell Gold/Silver.
I think it can reach 27mil, since I don't see BD/SP have much of an effect on it's legs.
The big question is wether Legends: Arceus is going to have an impact on it's legs.
I think not that much, since it's quite different, but we'll have to wait and see.

I think SWSH will reach around 27M and have better legs than Pokemon games on prior handhelds because each of the main series Pokemon games are different in artstyle (and this helps each of them actually) and the third version being DLC helps as well.

Ultimately, I still don't think SWSH will outsell RGB, but wouldn't rule it out totally. I think it will at least pass 25M. Kind of hard to imagine it not selling another 4 million over the next 5 years or so when even the 3DS main series games add a little bit to their total 5+ years later.

The only thing that could have hurt SWSH would have been a third version, but that obviously won't happen. Even a new generation on Switch (likely Holiday 2023) won't hurt it too much because SWSH has its own region and usually the initial generation sells more than the subsequent one.

I said 28-28.9 million as I figure next year sales will fall off with two new pokemon games and it'll slowly move from like 24 million to 28 million over the next few years.

Pokemon is barely a game franchise and more a media and merchan franchise. They aren't competing with GTA, but with Star Wars and Marvel Comics  

Many still don't understand this.

I don't think we can compare past sales trends with Switch sales trends. Handhelds always seemed to drive more of a "dedicated" fanbase, Nintendo consoles have been more viewed as "gimmick" than gaming machines for a while, etc.

The Nintendo Switch has been bucking all trends because it is truly the most innovative gaming hardware of all time. I personally have always dreamed of the ability to play a game on the go then when I'm at home play it on my big ass TV... I never thought it would be possible anytime soon... then the Switch came out. It is that rare moment where people find something they never realized they wanted it until they tried it. We haven't witnessed something that shakes up an industry this much since the original iPhone...