Oh it was definitely a bit of both, mate, at least in my opinion. He was unlucky in the CL draw on one hand (not to mention THAT disgraceful match that should not have been against Galatasaray), but on the other he also failed to win the Coppa Italia in any of his 3 seasons at Juve despite being massive favorites for it in his last 2 seasons there. Yes, Juve had a sort of mental block for winning that 10th Coppa Italia since the late nineties, but Conte as well frustratingly refused to adapt his team according to the strengths of Napoli and Lazio.
Imo, the matches against Belgium and Spain show a level of reading and understanding of opposition teams better than he ever showed at Juve which would suggest that he has evolved in that respect..