It's not about whether he should help or not, of course he should. He's a rider and he must listen to team orders. But I'm questioning team orders here, I think they were wrong. Gain was minimal, and loss was way bigger than gain. Simply timing was wrong, they should've called him way earlier, immediately when Quintana went with Pogacar, or not called him at all.
You mentioned Scarponi/Nibali situation in Giro 2016. That was different, it was quite far from the finish, and they called him as soon as it was clear that Nibali broke from Kruijswjk and Valverde. Timing there was perfect, Valverde came really close, some 15 sec if I remember correctly, but couldn't make a connection. The gain there was maximal, Scarponi was eating a wind in the valley, Nibali was sheltered and thus fresh as possible for the final climb. That was good timing and good decision.
I would rather compare this case with Landa/Aru situation in the Giro 2015. Now that was bad timing, and very bad decision.