That's all nice but has nothing to do with generations. A systems's gen is set in stone the moment it releases. Switch came too long after the start of the 8th gen, therefore it's 9th gen. Ps5 and xsx are coming too long after the start of the 9th gen, therefore they will be 10th gen. Eventually everyone will agree on that due to different reasons.
Nobody will ever agree with that nonsense.
The Dreamcast is universally recognized to be 6th gen despite launching three years before the GameCube and Xbox. A few extra months on top of three years between Switch and the PS5 and XSX aren't a problem when it should be clear to people that generations have gotten a bit longer. When generations themselves get longer, the launch timings naturally have to have more wiggle room as well.
3rd gen: 1983-1986
4th gen: 1987-1990
5th gen: 1994-1996
6th gen: 1998-2001
7th gen: 2004-2006
8th gen: 2011-2013
9th gen: 2017-2020
The launch timings of major consoles of any given generation are only messy in the early stages, but especially early on it was an "anything goes" because it had yet to be figured how video game consoles can be turned into a sustainable business. There's an omitted generation (Atari 5200 and the like) in this list, but it needs to be remembered that this categorization is a construct built by the gaming community, not by any console manufacturer. The reason for this omission and the subsequent stuffing of that generation into 2nd gen has to be because this lost generation had no winner and that's no good for the endless narrative of console wars.
If anyone has an issue with 9th gen launch timings stretching from 2017-2020 because that's too long of a timeframe, they should ask themselves why they'd want to advocate for 2011-2017 for the 8th gen.