Both Lago Serru and Courmayeur were tactically bad. And before the Carapazbestgetoveritcrew gets onto this, yeah he was the best those 2 days, but throwing away 50s to Majka who got rofldropped every other mountain stage means it was incredibly tactical. Courmayeur was just adding insult to injury and I don't know what Nibali was doing there.He tends to crash on wet descents (Rio, Angliru stage, Giro 2013, Firenze) so I think Mortirolo was a wise decision. Looking back I think he lost the Giro on Lago Serru, a combination of finding himself in the wrong place with the wrong companion on a not-so-good day.
Nibali was clearly on his worst day on Lago Serru, but he severely overestimated Roglic, and tbh the first signs of that were already there on the stage where Dumoulin crashed and Nibali lost additional time due to Pucchio.