I didn't just define it by power. Switch launch is 3yrs 8months apart from PS5/XSX launch. The Wii U was a failure that Nintendo literally discontinued entirely 2 months before the Switch launched. They completely started over. 8th gen is historic for 2 things - mid gen major upgrades to consoles, as well as a competitor releasing a 2nd console in the same generation to replace the first console due to failure. People actually trying to say the 9th gen started with the Switch in 2017? Or XB1 S/PS4 Pro in 2016? Its just funny to me.
What I find funny is that Switch will most likely be up against the PS5 and XSX for more than half its life regardless, and yet some people are still in denial about it being gen 9. Especially if the Switch gets a mid gen refresh of its own, your entire argument goes up in flames.
Again, Nintendo did not "start over" in gen 8. MS and Sony just waited longer to move on due to their mid gen refreshes. The WiiU being a failure has nothing to do with that.