The others consoles weren't supply constrained in 2018 neither it was the Switch peak year.
Obviously, PS5 and Series X|S weren't in the market back then, and weren't going to be released next month. PS4 and XBO were already in the declining part of their sales curve and didn't have the handheld market to rely on. When making comparisions we have to see the whole picture.
It's like saying 'PS4 sold way more units than Switch until now'. Obviously, because it has been in the market for way more time. When comparing PS4 (or Switch, or PS5, or Xbox) sales would make more sense to do it considering the whole picture, like their life cycle and competition context and/or launch aligning.
If we launch align global sales PS4 and Switch we see that outside the extra Q3 that PS4 had they had pretty much the same sales until the covid lockdowns (+AC in case of Switch) peak all gaming and internet industry experienced starting this spring, so until now PS4 had the launch aligned lead and now Switch has it (PS4 had the covid peak on its 8th instead of 4th fiscal year, and its peak is lower because it's in the sunset stage of its sales cycle, where it has way less sales so its peak is smaller and with its succesor being released on a few months, so many people insterested on a PS may have waited).
In the current November, Switch is in the context of its peak year for whatever reasons (covid, AC...) when even Nintendo thought its peak fiscal year was going to be the previous one, and Sony and MS are in the context of making their record worldwide launch (for MS in case of MS, for the gaming history in case of PS5) in more countries than ever before -so had to spread their available units between more countries- in the middle of a pandemic, and sold out all the units they could produce so couldn't sell more because of that. And the Xbox and PS5 warehouse/retailer stock and shipments were full of them so had very little space for their previous gen consoles.
So yes, looking at the big picture makes sense Switch is the best selling console now and some time ago, and will be the next month too, because even if there is a huge demand for next gen consoles they just released so their production capabilities are very limited compared to a device that is on its peak point of the life cycle so can produce way more units for each month.
PS5 maybe will have this December the best 2nd month ever sales for any gaming, or best first two month ever sales, but they will continue having a very limited supply because their production will continue being very limited and way under the current global demand. And PS5 is a console on its 8th fiscal year recently replaced by its successor, and way fucking expensive for being that old, so doesn't make sense to expect big PS4 sales from it this December. And well, Xbox has a smaller market share than PS.
How can this be?
Switch sold 1.3 million units.
PS4 sold 1.5m+ consoles in November 2013.
how can PS5 have the most successful launch, if it sold less than switch in November? Doesn’t make any sense at all.
Regarding PS4 November 2013 sales we only know it sold "more than 1M on the first 24h". We don't know if they were able to receive and sell more units during that month.
Switch in November 2020 sold 1.35M, and we know PS5 sales are between PS4 Nov 2013 sales and Switch Nov 2020 sales.
So PS4 November 2013 must have been between 1M and 1.3M. I'd bet PS4 November 2013 were 1.1M and PS5 November 2020 1.2M or something very close.