I agree with the person who mentioned Nibali as overachiever. None of his 4 GTs were won against a top GT talent in his prime. He never beat a prime Froome, Contador, Andy Schleck, Quintana etc. To win as many GTs without beating this caliber of riders definetely can be seen as an unusual tendency to be in the right place at the right time. The same goes for his MSR win as riders of his speciality can't really win this race without hesitation in the peloton.
Thing with Nibali is that he was unlucky or made tactical mistakes just as often. Crash in the olympic road race. Gifting time to Carapaz in last years Giro because he is focused on a battle vs Roglic. Running into GOAT Horner in the Vuelta. Losing Liege to Iglinsky (clinic).