Year 4, Switch released in March 2017, it's in year 3 now. A 3rd year peak followed by a small decline in year 4 is a pretty normal sales curve.
2013 2014 2015 2016 2017(peak year 5) 2018(sustained peak) year 6
ps4 peaked year 5/6
so switch peaking in year 4 is pre mature.
It released in mid-November so counting 2013 as year 1 makes literally no sense at all. Also 2018 had a 10% decline, that's not "sustaining its peak", thats a decline.
Besides, who cares when PS4 peaked? It had a later than normal peak, good for it but peaking in year 3 or 4 has been a very common thing for consoles.
What are you getting out of making nonsense arguments?