[drumdance]

"The more responsibilities an object has, the more complex its behaviour becomes, and is therefore more difficult to prove and reason about."

Emphasis mine. I don't think this has to be true. Yes, models get fatter, but the responsibilities will have to be implemented somewhere and to me it's simpler and easier to debug when it's as close to the domain model as possible instead of in some abstract/generic model.

Of course, if you have policies and services that apply across domains, then by all means break them out and recompose as necessary in the the models