Long time lurker with some thoughts.
Judging by the general attitude, I'm pretty sure there is no way Vingegaard and Roglic win over people's hearts in this situation. If they race, people act like many of you are doing now. If both had focused on neutralizing the stage for Kuss, then people would be castigating them for not racing. Either way, they'll be criticized.
The criticism that Roglic chose to stay with Kuss yesterday and that Vingegaard should have done the same today is rather absurd. Roglic did not chose to "help" Kuss - he tried to attack, but could not bridge the gap to Vingegaard. If he could have, he would have. He just did not have the legs yesterday. Today Vingegaard had the legs to follow Roglic. Personally, I think he could probably also have dropped Roglic, but chose not to - 1) because following on Roglic's wheel to gap him at the end would have been an actual nasty move, 2) Vingegaard already has 2 stage wins - no need to be greedy, and 3) I think he honestly doesn't mind giving Kuss the Vuelta win.
I think it's weird that people try to find ulterior motives in everything these guys say, rather than just accept that - perhaps - they might be telling the truth? Both can be telling the truth and race like they did today (and yesterday).
I think Vingegaard mainly wanted the stage win yesterday - I don't think he expected to gain so much time yesterday as he did - as many have noticed, this came out as much from the other teams being weak/tactical than pure strength over Kuss. And I think his ride today shows he is in two minds - on the one hand, he can't stay with Kuss when he is obviously stronger - that would make the gift very obvious (and Kuss doesn't want gifts), but on the other hand, he's not willing to push 110% to get the win.
It'll be interesting to see how the final important GC stage goes, but I think Vingegaard (and Roglic for that matter) are riding the way they do, not only because they have huge egos (which you must have to some extent, to be a champion), but also out of respect for Kuss. Think to the alternative scenario, with Roglic and Vingegaard both riding purely as domestiques for Kuss. I don't think anyone (other than Americans) would love that. Kuss would win, yes, but there'd always be a huge asterix next to the win and people would say it is undeserved (i.e., he only won because Roglic and Vingegaard let him). If Kuss manages to defend the jersey tomorrow, people will still put a small asterix by his name but at least no one can say that the win is not deserved.