Doing 1m dps is doing 1m dps. Doesn't matter what spec you are if you're doing 1m dps which is almost double what you need to do in Heroic. I linked logs showing this.
Also i like how you say Assassin is fine as well in addition to Sub when Assa is just about equal in usefulness as Outlaw is which just goes to show you don't know what you're talking about.
Now that I think about it, all three rogue specs are going to have issues damage wise come Antorus. None of the specs scale very well, including sub. In fact, when looking at logs, sub has slowly been dropping down in the rankings. So either Blizz will have to bandaid buff all three specs, or do something to fix rogue's scaling, or else the class will be in a bad place in terms of dps.
Warcraft Logs Analysis. I said just about equal not equal. Outlaw comes ahead on 4 bosses, on 2-3 bosses outlaw is lower but practically equal with Assa, and on there's 2-3 fights that Assa is way ahead. Assa is still overall higher, but its not nearly to the level people are making it out to be.
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No chance of blizzard fixing the scaling issue before next expansion. They don't care about rogues enough to put in that much work before pre-expansion patch. They'll stick to bandaid buffs like they've treated Outlaw the entire expansion. They at least tried with Sub, and it worked for this tier, but to extend that to the other 2 specs? I don't see that happening.
For heroic if your ilvl is fine and you know how to play your spec, then you will always be a great asset to a raid. Rogues are amazing at doing mechanics and just surviving which is all what heroic is about.