Gens are a bad concept to use at this point. In fact really even in the past gens have been such a nebulous concept, to the point that for example Second generation seems to span 1976–1992, Third generation 1983–2003, Fourth generation 1987–2004. It doesn't really make any sense.
Normally we have compared consoles to consoles and handhelds to handhelds, and tried to lump gens by proximity and tech. Switch is a hybrid which cannibalizes both markets, which makes it hard to compare apples to apples.
Switch is going to fairly neatly fit half it's lifespan during the '8th gen' with PS4/XBONE and half is lifespan during the '9th' gen with PS5/XBX, yet be considered 9th gen?
Other than a few added bits of tech, granted really good tech, like ray tracing and SSD. PS5/XBX are going to be iterative at best and with the XBX at least will be 'backwards compatible', although really it's just maintaining the same kind of compatibility PC games have enjoyed for a long long time. PS5 could be the same. It's like another refresh, like PS4Pro and XBONE X. Unless Nintendo decides to gamble yet again and potentially pull another Wii U, why not just release a Switch New (Switch 2023-24) that is just a bump like the PS4Pro, and XBONE X, forever.
What happens further down the line when more and more of this stuff is in the cloud and all these games, perhaps not Nintendo, can be played on any device with the only restriction in fidelity being how good your internet and screen is?
If we are going to continue to compare devices to devices, lets just drop the gen moniker and compare as is. We currently compare PS4/XBONE/Switch as a group, even if many people consider Switch next gen. And when PS5/XBX release still compare with Switch as well. Focus on launch align trajectory, sales gaps, software attach, etc. Not whether they won a gen or not, but rather if they are winning the this weeks/months sales.