People say that Samsung software is disappointing but that can mean different things:
1) Does the software slow down compared to the Pixel? Yes, for sure.
2) Is Samsung's take on Android a far more mature offering with countless useful tweaks that stock Android simply doesn't have on Pixel? Yes.
One day I'll make a list of the best features of Samsung's software that the Pixel misses. Really basic/thoughtful things.
At the same time, Samsung misses on the core stuff. Like you can't turn on WiFi or turn it off without bypassing the lockscreen. No lockscreen text replies either. Stock messaging app is also pretty meh since it asks for default contact numbers repeatedly. Bixby takes up too many resources as well.