Allegro is a JJ legend, nothing can change that and he actually left on decent terms in the end. Winning a trophy and taking a minimal severence package.
But I don't remember another high profile coach fall off so quickly. Went from one of the top coaches in Europe to a Del Neri regen. Even Mourinho's decline was gradual.
I'm sure he'll stick by his 'philosophy' in his next job too but he shouldn't be anywhere near a big club again.
I think it was exacerbated by his determination to do things his own way in the face of all cricitism, like his personal mission was to commit to his ideologies to the greatest extent, absolute stubborn shithousery. And then he realised that he probably wasn't going to be retained and Giuntoli wanted his own guy, we won the Coppa, and there was that crazy release of emotions where he lost the plot as he probably felt like he had "won" the moment.
I don't believe in another scenario he'd be quite so destructive or stubborn, wouldn't even surprise me to see him have a bit of success elsewhere, but you can see that his ideas are far removed from what we would consider modern football.