Yes I would! The Series S is a great Assassin's Creed machine as long as you don't mind a lower display resolution. You'll also see some weird cloth physics issues in Origins and Odyssey as the "next gen" patches doubled the framerate without doubling the rate of physics simulation, so things like flags and clothing have a stutter. But that's a small issue.

Many of the older games got FPS boost upgrades as well:

https://news.xbox.com/en-us/fpsboost/

I completely agree about Unity. It's still a remarkable looking game. If it hadn't launched in such rough shape then I think the franchise as a whole would look very different right now.