I feel like just as a lot of 360 owners went onto PS4, a fair few Xbone owners will get a PS5. It could make up the difference with a better lineup of games, but as of yet I just don't see any solid indication that XS will sell better than Xbone. Game Pass didn't exactly change Xbone's fortunes, and the Xbox brand lost a lot of its mojo and coolness with the Xbone.
The launch-aligned graph was posted above and the XS's momentum is notably better. That's why it's on pace to hit 5m in week 30 or earlier whereas the Xbox One needed 37 weeks to reach that mark. The reason why the XS's gain was modest over the last month is because of Titanfall which provided a much needed boost for the Xbox One.
The Xbox One's sixth million took only ten weeks to achieve (the fifth million took 17 weeks in comparison) and that's because of the first official price cut and the launch in the remaining notable countries of the console market that fall roughly into the timeframe of the path to the sixth million. Still, the XS should hit 6m earlier than its week 47, by a few weeks. That will mean staying ahead despite its predecessor already receiving a price cut which has similarities to the early Switch vs. 3DS comparison, albeit on a smaller scale. Regardless, the result will be that the XS breaks away from the XB1 line during year 2 because the similar sales during year 1 were achieved under different circumstances, ones that favor XS.
Of course the XS won't beat the XB1 by the same magnitude as Switch will outsell the 3DS, because the XS hasn't as much going for it as Switch does. But the underlying point is that especially in year 1 one has to account for the factors that led to the resulting sales, because otherwise you'd conclude similar lifetime sales based on similar lines despite known factors for a differing sales potential.