Well, as some non-Nintendo fanboys already stated: the sales are dropping fast. You can predict the sales by looking at the graphs that show monthly sales and if it continues like that, the switch will sink so low that it will have problems after selling 150 million + units. They need a really good christmas but who buys a switch nowadays? Whoever wanted to safe princess peach from a castle or princess zelda from a high tree again and again and again already did that. And the switch needs to pass 160 million by far to have the number 1 spot without a doubt. Good luck.
And even if the switch manages to do that: its like comparing the highest selling games of all time. You got Minecraft, GTA V and Tetris. The revenue makes the difference. Is it a bigger success to sell 200 million + GTA V that were sold for 50-70€ ($) for many years or to sell 300 million + copies of a 10€ low budget title or 100 million + Tetris games that were shipped with the gameboy in a bundle?
The PS2 was always a very high price highend console, The switch was always that cheap family toy it is today. Maybe the switch 2 only costs 150€ and sells 200 million and the PS6 600€ and sells only 80 million, Who knows, but its not a fair comparison. Oh, and how about the markets? The PS2 was sold in less countries than the switch and when did the switch have its best year? During Corona... What an advantage. As you can see: even if the switch surpasses the PS2, which is unlikely, the PS2 would still be deserve the title "king of consoles" for me.