I personally liked sub initially in BFA. Aside from the early expansion AoE cheese for buffing ST to ridiculous amounts I thought it was a good spec. They got rid of the little things that made the spec harder to play while still maintaining more complexity than Sin or Combat. I just did a RF and saw a sub Rogue with better gear than me do 40% less than damage. IMO, all you have to do is look at Demon Hunters and their success as a DPS. They’re successful because they’re new and fit the vision Blizz has for the future of the game.
You look at the majority of classes that have gotten overhauls the last few expansion and look at where they are now. Who’s topping damage meters? Who’s dominating the brackets? Not Sub Rogues. Sub Rogues have a very antiquated toolkit, which for the longest time was balanced around Preparation, which they no longer have. Too much has been taken away from them in the efforts to homogenize the game. This is most evident with the low skill tiers, where poor mechanics and decision making are punished without mercy. Versus those same players switching to Sin, which is much easier to play and they immediately become better players.
Sub is, I think, the only remaining spec in the game to not receive a real rework. They’ve been gutted and received very little in compensation, which is why it’s not very good. Certainly, we could say they nerfed this and that, but DHs get nerfed and they’re doing just fine. Why? Because they check all the boxes Blizzard has for creating something successful. It comes down to a lack of modern fundamentals.