I'll just ignore the original post because of its questionable logic and instead focus on the question the thread is asking.
2020 can be expected to be better than 2019 because of the effects of a console revision and a price reduction lasting through the whole year, but that doesn't mean 2020 will be the peak year. Aside from people commonly forgetting that Switch's stake in the handheld market can't be fully realized until price has come down to an appropriate level (a sub-200 dollar Switch might not be available before 2021), another very important factor is that Nintendo has now only one console which changes things significantly.
Previously, Nintendo's top development teams had to go back and forth between two consoles to boost their sales which resulted in a loss of momentum for both consoles at different times. Breath of the Wild 2 is just the beginning of hammering the point home that one console is much easier to support. The teams that worked on MK8D/ARMS, Splatoon 2 and Super Mario Odyssey also have another Switch game in the pipeline, so there won't be a sudden shortage of system sellers like on previous Nintendo consoles, with the exception being the NES because that too was Nintendo's only console at the time.
There are also a multitude of 3DS game developers, both first and third party, who have been slow to transition. Switch will have a very robust software lineup for the next few years, so that creates a very appealing console in conjunction with the right price. The timing of revisions and price reductions is still up in the air and as long as Switch sells as well as it does (there's already growth in year 3 despite neither a revision or price cut), Nintendo can postpone those things and notably extend Switch's lifecycle in the process. 2019 won't be Switch's peak year and 2020 might not be it either.