I think this is the first test for Pirlo as a manager on a big stage like UCL.
First but a big test.
If i'm not wrong, Zidane starting from Real Madrid reserves team before he managed Madrid main squad. He still have a time to learn how to manage team before promoting as head coach for main squad.
You are right about Zidane. Zizou managed the Real Madrid reserved team and he tried to give opportunities to his children. After years and seasons, Zizou's children did not show their ability to become good players (not say become legendary player as Zizou). They failed to get positions in squads of clubs they are playing for.
Right, it's a start and I think the fault isn't just about the coach because the performance of the players has to be taken care of too, just look at other teams with great coaches who are more senior doesn't even look okay. In every match there will always be wins and losses, besides that the absence of CR7 and Alex Sandro also affects the team's performance to play better. In contrast to Barcelona, although Coutinho and Pique don't play but Barcelona have second tier players who are also good in position. With that, this defeat is natural I guess.
CR7 is a key player of Juventus but he is getting older and older. I see drama that CR7 will leave Turin after this season. Pirlo and Juventus need to have plans without the appearance of CR7. Juventus performance (good or bad) is result from their squad, not only from Pirlo or from CR7.