Yes that is indeed how the canon works. Our timeline is the prime timeline - so it has the most weight. That the other Garroshes are heroic, doesn't mean they are without sin either. Question is also if he is in Revendreth by design of the purpose, or by the machinations of the jailer & co to use him as an anima-battery like Kael.
I would imagine Garrosh being a raid encounter, but similar to Kael in a redemption/rescue mechanic.