I just looked it up, and the DS sold 30+million units during its peak years, something the Switch hasn’t accomplished so far. It’s easy to forget just what kind of monster the DS was (and it was a handheld only!).
It also makes me wonder if the Switch won‘t catch up to the DS (and PS2) after all, unless they manage to sell >20 million annually for a couple more years. The DS really started to decline in its seventh year, and fell off a cliff in its eighth. If the Switch follows a similar trajectory, sales should remain somewhat stable in 2022, then significantly decline in 2023, before plummeting in 2024. It‘s probably going to be really close; I expect the Switch to land somewhere between 150-160 million when all is said and done, leaving it either slightly below or slightly above the DS and PS2.