I see, thanks. My original interpretation was that by "separating data from logic" you meant data-oriented programming where you intentionally give up on encapsulation.

"which is that if you're passing behavioral inheritance from a "server" to a "client", then it gets harder and harder to predict how that client is going to use it"

You mean a "server" returning the base class object whose methods are overridden by a successor class known only to the "server"?