All abilities that aren’t simply “do X dam” are maintenance for every spec. There’s zero point in designing specs that only “do x dam immediately” over and over with zero nuance in the gameplay and it merely becomes a “press buttons as they light up” spec. That’s how you get BM Hunter. I don’t want Rogue to become BM Hunter.
Even if it adds ‘nothing’ (which I assume you mean it doesn’t add any extra ‘brain power’ for a skilled player), what it does is keep the skill expression between a bad Rogue and a good Rogue at a modest level. One of the reasons Sub is very beloved by vets of Rogues but maligned by newer Rogues is because of the skillcap around Shadow Dance since its inception. They’ve done a lot to reduce the skill requirement to effectively use Dance, but they could just as easily remove Dance and bake all that extra damage into Backstab/Eviscerate and make the spec a 2-button spec like Assassination used to be with Cut to the Chase. We can both agree that isn’t how Sub should be designed, and imo Assassination should move away from the slow, monotonous design as well and be forced to keep a lot of maintenance finishers up so the spec feels more ‘full’.