Wii has one more significant holiday season then levels off; it all comes down now to how much stamina Switch has beyond 2022.
I don't get why you are so damn pessimistic so often. While Switch's holiday sales in 2021 will be a bit lower than expected, its LTD in the USA will be ~34.5m by the end of December already. Afterwards it's only a gap of ~7.20m left to go which can be accomplished by the end of 2022 if things go well. Sales in 2020 were ~9m, sales in 2021 will be 8.0-8.5m. A decline in 2022 is likely, but that's not a problem.
It's a done deal just like Switch vs. PS4 worldwide. The remaining question is by how much Switch will win these comparisons.