Unless they keep producing and selling Switch for 12+ years like Sony did with PS2, or their next system tanks out of the gate like PS3 did for PS2, or a huge amount buy Switch's for non-gaming purposes like tens of millions bought PS2 to be the cheapest dvd player they could find did, then it will never be a fair comparison. Switch will probably produce and sell devices 4-5 less years than PS2, will probably be followed by something with an attractive price point out of the gate (unlike PS3), and is used exclusively for gaming.
Because of this, I'm a lot more impressed by Switch selling 10 devices than PS2 selling 10 devices. If Switch we're to actually catch PS2 lifetime sales despite ps2's advantages, then in reality it will be much more impressive, not barely, than the ps2's success.
12 years isn't really needed to catch the PS2 as 20m this year and next puts its well with in range of PS2 to the point even below average sales can catch it all Nintendo needs to do is to keep Switch active, if anything only another 3 or so years is needed.