Sure, but Froome was lacking in the Dauphiné and not as strong in the Tour as previously, so he had a better buildup for a double.
Yes, whenever Froome made a serious, focused attempt at double GT’s he structured things very differently, eg riding himself into form over for the first week of the Giro. That’s not at all the same as being at peak consistently from day one and before across both GT’s, and all races in between.
I also didn’t get the impression that Roglic even planned to double up. I wonder if he’d even be at the Vuelta if he didn’t lose the Tour so dramatically and unexpectedly? Again, pretty amazing if this wasn’t part of his seasons plan but he’s able to just go again without any signs of accumulated fatigue from the Tour which was surely his primary goal for the year.