Integrate QuickSwitch into the OS
QuickSwitch is an app used in rooted devices to allow third party apps to have their app switcher be used by Android. It solves issues such as animations and such looking very wrong with third party launchers.
This would allow for CalyxOS to not have to worry as much about complaints when it comes to customizability; as a recommendation for a third party launcher such as Lawnchair would be enough, right now, it looks very out of place unless you use QuickSwitch which is a rooted thing.
There are of course still some complaints on AOSP' UI which would be outside of that scope, but basically 80/90% of complaints are things held in the launcher, or the app switcher, sometimes the notification bar.