The only console generation where one of the main competitors wasn't either shooting themselves in the foot or starting with a severe handicapp was the Megadrive/SNES generation. During the NES era the whole industry crashed and Nintendo came from out of nowhere to fill the void. N64 shot itself in the foot with carts instead of CDs, during the PS1/N64 era. Gamecube shot itself in the foot with tiny disks, and no DVD playback ability. Xbox started from the severe handicapp of being an entirely new player to the wars. PS3 shot itself in the foot at launch. XB1 shot itself in the foot with "always online DRM" almost being a thing on the console, and packed in Kinect driving up the price.
Maybe during the PS5/XB2 gen we will finally have a good fight. MS still has terrible 1st party output compared to Sony though. But then again Megadrive exclusives always paled in comparison to Nintendo exclusives, yet Megadrive took almost half the market from SNES. And MS has terrible 3rd party support when compared to PC/PS4. So even if we get a good fight I still expect a 40%:60:% market split between MS and Sony (not counting Nintendo or PC sales here). MS currently has around 29% of the PS4/XB1 market. MS would have to double it's 1st party output, stop making its 1st party games available on PC, and get those 3rd party games that come to PC/PS4, but not Xbox to finally come to Xbox. That's the only way they break past capturing only 40% of the Xbox/Sony market.
As far as Nintendo goes, they will continue to ride high. 60 million by the end of 2020 is pretty much in the bag at this point. They'll keep selling 10 or so million a year in 2021 and 2022. They probably won't quite hit 100 million lifetime, but that won't really matter because the attach rate for Switch games will be insanely high. In other words customers will be extremely satisfied.
