So I see on HOME page that Switch is very clearly considered as a 9th gen machine.
Please explain me your arguments (anyone, not only the person who made this new graphic) for putting WiiU on 8th and Switch on 9th because really, I still don't get it after 31 years into video games. No one has yet convinced me.
The idea of generations really only holds up well if appliedto one manufacturer. The PS4 was the next machine after the PS3, so a new generation. The WiiU was the next machine after the Wii, so it is a new generation. The 3DS is the next gen after the DS. You get the idea.
The moment you try to fit machines of different companies into one distinct generation and define overarching gens independent of manufacturers, you get into trouble. Yes, sometimes the release schedules somewhat line up, as different consoles tend to compete with each other. But that doesn't always work like that.
The proponents of clear gens tend to ignore 1st and 2nd gen and the lost gen. Because back then the lines weren't as clear cut. But even later some machines didn't line up as well. NES released in different regions at wildly different times. It released in europe more than 3 years later than in japan and only about 4 years before Super Famicom (SNES) released in Japan. So where does it belong? Where does the Dreamcast belong? How about the long tail of sales of the PS2?
The Switch is the successor to both the 3DS and the WiiU, and as handheld and stationary console already were not aligned, it was clear it wouldn't fit neatly into both timelines. As it is, Switch released right on schedule for a 3DS successor, but the life of the WiiU was cut short. A decision that was probably made easier for Nintendo, as the WiiU wasn't all that successful.
As I said before, competition made release schedules line up a bit. But Nintendo started at least since the Wii to diverge in their market approach. It is not like Nintendo isn't in competition with Sony and MS at all, but for the most part they doesn't affect each other *that* much. PS4 sold like it sold before as Switch released. Switch kept on selling as the PS5 released. That also makes it easier for the Sony gens and the Nintendo gens to not be aligned. Switch either reaches customers that aren't interested in Sony or MS offerings at all, but also customeras who happily purchase both. MS and Sony on the other hand are very well competing for the same market. That may change, with the increased focus of MS on Gamepass, and maybe in the future their schedules will also diverge to each other more.
An word about people that think gens are about tech: look at the history of consoles, especially older ones and see how wrong that assumption is. The only constant is, that the next machine of the same manufacturer will be a progress in technology.
So TL;DR: don't put your eggs stubbornly into the idea of defined gens independent of manufacturers. In reality the gens of different manufacturers only sometimes line up neatly.