Should Barcelona have not hired Guardiola? Actually, Juve is in a pretty similar position as Barca was when they promoted him from their B team. Sometimes you have to take a leap of faith. I have no doubt Palladino is an elite manager. Should we wait to see him take some other big club to trophies first, or should we get him while we still can? There will be risk no matter who they hire. I'd actually argue whiffing on someone like Zidane (aka expensive) would hurt the club more than whiffing on someone like Palladino.
For every Guardiola there is a Pirlo, Neville, Shearer, Henry, Seedorf, Brocchi, Montella, Di Matteo. Guardiola has also had some immense players to work with, from his very first job until now.
Sometimes you need to take a leap, we tried with Pirlo and it failed. But sometimes you need to assess the situation at the club, assess the manager and do what is best for both. Palladino could definitely be a top elite manager, but there is not much of a sample size to base than opinion on yet. He could also easily be a complete flop. In Scotland we had a young manager who won 2 domestic trophies in his first season of football management with a club with one of the lowest budgets in the league, something completely unheard of where we have 2 teams with so much more money than everyone else. He was linked with teams in England but stayed on. The next season his team was 2nd bottom, the next he was sacked.
I've been a fan of De Zerbi since he was at Benevento but I don't think he would have done a good job here after leaving them or even after Sassuolo as he would now for us. He is a far better manager now because of his experience there and with Shahktar and Brighton. If you put the Benevento De Zerbi in the current Juve environment the chances of him failing are high.