Yeah, Xbox vs Gamecube was close too. Just nothing of this scale before.

I remember the battle between the Xbox and GameCube. They were fighting over the scraps with how much ahead the PS2 was. 

PS3 and 360 were also fighting for second place. Switch vs PS4 though is just a titanic battle between two dominating supergiants.

PS2 and DS were also very close to each other. 154 vs 158M

Just for fun, here's what the gap charts look like when you align PS4's April 2014 to Switch's April 2017:

It only looks close, because 2018 was kind of a "meh" year for the Switch, so that makes the PS4 look competitive.  Switch is about to pull ahead of PS4 for good.

That's a bold claim; I don't doubt Switch will sell well this year and 2021, but I'm skeptical whether Nintendo will push it hard enough beyond that for it to match PS4's legs in the long run.

The Switch is actually a very different animal than a system like the Wii.  Nintendo won't support of it so suddenly like they did the Wii.  They only have to support one system at a time now instead of splitting resources between home and handheld markets.  Also Switch style games are a better fit for Nintendo's developers compared to Wii style games.  Their developers prefer to make these types of games.

If Nintendo are smart they'll push the Switch for years to come, but what worries me is Nintendo have a long history of being really, really stupid at times.

Yeah, I agree that Nintendo can be stupid.  The dumb thing I am more worried about is that the next console won't be a hybrid like the Switch.  It would be dumb not to simply have a Switch 2 replace the Switch when the proper time comes. 

But they have said that they plan to support the Switch for many years, and I believe them when they say this.