You're spending more for the Series S as soon as you buy the memory expansion. Or as soon as you buy around 3 games digitally that are $10 or less physically.

Also, there are currently only 3 games that your One S can't play. That's Scorn, Flight Simulator and Gotham Knights. Redfall is coming up but then there's Starfield and Elder Scrolls. Neither of those have a release date.

Save up your money and buy an X when one of those games drops. Right now, there really is no curren gen exclusivity with Series X/S.