Switch isn't selling on graphics so it won't matter how "outdated" it is in 5 years.
And Halo is not even remotely close to being a Pokemon counter. Even at Halo's peak, a decade ago, no game in the series has ever sold as much as the recent new mainline Pokemon titles, and the Halo series has declined considerably since then.
Have you looked at the weekly charts recently? Switch is outselling Xbone by close to 2-to-1 even with severe supply constraints and a higher price, and Switch is just getting started while Xbone has already blown its load.
I like my Switch, i think its a great system. However the X1 is still selling. We dont know the exact figures as MS isn't telling anybody. Saying the X1 is getting destroyed on sales is again speculation and not actual figures. Nothing is official.
As for Halo, the franchise mainline games can sell up to 10m units. How is Halo on the decline? because of one entry? Halo 4 sits on over 9m copies and possibly 10m by now which outsold Halo 1 and 2. That isnt a decline. They had one of the best selling Halo games recently. Sure 5 went downhill mainly due to the direction and decisions which wont be happening with Halo 6. I never said Halo will outsell Pokemon. However its a juggernaut franchise that with protential can sell double digit millions and will push Hardware.
Remember the Xbox also has massive Xmas sales and is attractive for the 4k market which will be big in the next few years and houses the big 3rd party games. Switch will sell well for awhile however its New, its still selling based off hype and the fanbase. X1 is in its 4th year, its sales will start to look small by now however there are heaps of reasons for them to raise. As an over the top example - Sea of Thieves might be the next Minecraft, we dont know. All i can say is dont base your judgment off the sales charts when one number isn't even confirmed by MS.
I see Nintendo releasing a new system in 2021 which will replace the Switch while X1X will continue to push X1 sales same goes for X2. Thats my prediction.
The most logical reason MS aren't releasing numbers is because the numbers are not good. If Xbox One was doing well, they'd be bragging about it.
The sales of Halo games have been in decline since Halo 3 in 2007, with each entry selling worse than the one preceeding it. Halo only crossed the 10 million mark once, and those days are long gone. Neither Halo 6 nor Sea of Thieves will alter Xbone's trajectory significantly, just like Halo 5 didn't, Gears of War 4 didn't, and Quantum Break didn't.
Xbox One X is too expensive to make a big difference, people will just buy the PS4 Pro instead. While Switch has carved out a niche for itself, Xbone has to compete directly with PS4, and is getting its arse kicked.
And why would Nintendo replace Switch after only 4 years? MS are the ones with a motive to replace and move on sooner.