Been noticing a lot of destruction locks on logs prioritizing mastery over intellect now in gems, reforging, etc. Is this viable at a certain ilevel or does it just depend on what gear you have? I pull my fair share in raid with int over everything but am always looking for ways to improve. Looked for a good thread on it but haven't been able to find it. Any comment appreciated!
I would take a wild guess that OP is asking it after seeing many top warlocks going for int/mastery or pure mastery rather than Int, after a certain threshold one of which is obtaining a legendary meta. None of it mentioned in the guide you are referring to.
I can confirm that at some point secondary stat becomes more powerful that intellect when it comes to gemming. Simming is not a perfection but still can help a bit to see when the case is true.