In the here and now though, I very much doubt there are a lot of people out there who got an Xbox Series S and weren't happy with the purchase. A solid first year library, the value of Xbox Game Pass, and the console's cheaper price point are all crucial factors that have contributed to a great first year for it.
In the short term, we can probably expect at least 2022 to be another great year for the console- in fact, looking at how stacked 2022's lineup of games is, it's probably going to be a much, much better year for all consoles on the market. In the years beyond that, it's hard to be sure right now exactly how the Xbox Series S will fare.
Microsoft certainly seems confident in the console's ability to continue to be a viable alternative throughout the course of this entire console generation, and we certainly hope that turns out to be the case.