Sounds like too much effort to prove something that you aren't fully contesting yourself, hence why you say "almost all deals" and "mostly towards Xbox, not Switch."

Calling the market share stable doesn't sound right when Nintendo went from ~60% to ~80%.

As for a yearly breakdown, Switch will end 2020 at ~17.5m (I hope I am remembering this correctly), so going from there I see it selling something like 5m, 4m, 3m, 2m and then fizzle out over the following years. In Japan Switch is closer to the saturation point than anywhere else in the world, so a steady decline has to be expected despite revisions and price cuts in the coming years, unless Nintendo puts out a revision so substantial that they'll get a high repurchase rate. Whether they'll be able to pull that off is up in the air, hence why I said 30m+ and not ~30m.

You wrote down the disclaimer that PS2 sales are excluded, so I wasn't going to pretend that the 2006 and 2007 splits are correct. Prior to 2006, it wasn't that great of a time for Nintendo either. We have lifetime figures of 20m PS1s and 23m PS2s vs. 5m N64s and 4m GCs plus 16m GBAs and... I don't recall how much the GBC sold right now. But when you have these numbers as a basis and then spread them over the course of a good decade, you'll get nowhere near 80% for Nintendo in any year, plus it actually gives Sony a higher market share in some years. (Sega was there too and had a higher presence than the Xbox afterwards, but it's not that important.)

As for Sony winning a year with the PS5, that's a longshot. The PS4 peaked at ~2.0m and it's hard to imagine that the PS5 can top that.

You are correct that there are fluctuations in market share due to transition periods for both companies, but it's apparent from the numbers you posted (they are complete for the transition from gen 7 to gen 8, and the transition from gen 8 to gen 9) that the state of the market has swung more in favor of Nintendo from one generation to the next one. The previous time Nintendo topped out at 70%, this time they got to 80%.

EDIT:

@Farsala , I found this video, covers market share for the years 1996 to 2007, so starting at the point where the PS1 got traction. Start of the video until the 6 minute mark is the elaborate version with system breakdown. 6 minute mark until the end is the short version with only a manufacturer breakdown. Sony had the majority market share from 1997 through 2005.

PS sales aren't declining in Japan because of a major loss of interest in console gaming, they are declining because people buy Nintendo consoles instead.

Looks like you have trouble to keep your bias in check. You keep insisting that Switch sells because it's a handheld, then turn around to admit that the hybrid sells more because people want to play it on the TV.

RFA will keep selling and will eventually reach Wii Fit numbers. You said motion controls were a fad, yet here we are and have a game that people like you would have predicted to have no chance to sell 10m+, but it's already safe to say that it will clear that bar with ease. Calling Labo a big motion control initiative shows a severe lack of understanding on your part; Labo was a product very similar to Wii Music, more toy than game. Wii Music couldn't achieve success during the peak of the Wii, unlike later games like Wii Sports Resort and Wii Fit Plus. Also, what's the sudden difference between motion controls and fitness appeal? In your mind it was all a fad anyway, with distinctions only becoming necessary once your simplistic point of view begins to show a lack of coherence.

I think you're the one not keeping your bias in check. Do you honestly think if the Switch was twice as powerful, but only a home console, it would have fared as well? Hell no. It's because it's a handheld that people can play on the go and easily hook it up to the TV when at home. You also have the multiplayer on the go with the Joycons.

And we'll see how RFA continues to sell. Right now it's at 5.8M after a year. Wii Sports Resort was at 7.6M after 6 months. I highly doubt it reaches the 33M of Sports Resort. Even more unlikely to hit 42M that the Balance Board did.

And funny that you just dismiss Labo as Wii Music. Nintendo thought it was going to be a big hit and push HW sales while they had a slight drought in SW output. That obviously didn't happen, causing them to miss their quarterly projection. It's obvious they had big plans for it with more kits. Maybe it would have done better if they acted like it was for fitness.

The PS4 sold more units than the Vita, so an inherent immense advantage for handhelds does not exist. Rather it's an often used excuse to explain away Nintendo's continued success in the country while it frames Sony's situation as being one that is out of Sony's control.

Moving interest has first and foremost to do with the quality of game libraries, because with that explanation you achieve logical consistence across hardware form factors and generations. The PS4 sold more than the Vita because it had a better game library than it, the 3DS sold more than the Wii U for the same reason, Switch will handily beat the PS5 for the same reason. It obviously helps Switch that is both home console and handheld console, because the flexibility in how you can play the system is an inherent value, but the most important factor for its success is its robust game library. That's why its sales can keep up with the 3DS and will soon pass it launch-aligned despite a notably higher price point and far fewer revisions over the comparable timeframe.

If you go further back in the generations, you have the DS and PSP which first made handhelds have higher hardware market share than home consoles. Both of them had much more quality and quantity in their game libraries than previous handhelds because game development costs on home consoles had hit a breaking point, forcing many developers to examine their opportunities elsewhere. The generation before (PS2, GC, GBA) didn't have this issue, so the PS2 had it easy to amass a much bigger game library than Nintendo's consoles. Unsurprisingly, every generation before 2000 played out the same way.

In a way the form factor of hardware does matter a lot in Japan, but it's not that Japanese gamers have something against playing games on TVs, rather it's that the evergrowing game development costs caused a change to the previous reality that home consoles would get the lion share of the software, and then gamers followed the games. This can once again be observed with Switch sales where the hybrid SKU has comfortably outsold the Lite and the only reason for the Lite's competitiveness was prolonged limited stock for the hybrid SKU. If handhelds were what Japan inherently prefers to play on, then the Lite should sell far better due to its price.