If you look at Millers and Cabaniss, you can see that they bring in outcrosses on occasion ,both complete unrelated and somewhat related. It would seem that both worked for them. And it seems that they usually use sons of the outcross sire heavily .
At some point ,your sheep need an upgrade, and an outcross is likely the way to do that.
When is that time? Good question.
Copy a breeder or forge your own path? Again topic for debate.
Most top breeders are forging thier own path and building thier own "kind" ,in my opinion. That is what makes thier sheep "different" and creates value for them.