We went through this already before. Pirlo was even more finished than Seedorf was at Milan and Allegri didnt manage to get anything out of him. Conte rejuvenated him and built the team around him and Prandelli followed suit with Italy.
Pirlo was plagued with injuries in his last season with Milan, was 3-4 months on the sidelines iirc. We made shrewed business there, as he got back some of his form, but that was far cry from Pirlo between 2002-2006. Conte did help him, but Pirlo more than anything needed change of scenery.
Marchisio was an absolute nobody without a single decent half season under his belt. If anything Giovinco was seen as the really promising one and marchisio was only seen as a squad filler. The current season is his second great season in all of his career if you haven't noticed and the heights he reached since Conte were much better than anything he did under any other coach before then.
Marchisio was starting CM for Italian NT or thereabout, so wasn't exactly a nobody as you've put it. I rate currrent season more than 2011/12, as he's been consistent throughout whole year.
Barzagli was even more of a nobody that he couldnt get a starting spot with Wolfsburg in his last two seasons. Prior to 2008 he was at best an Azzuri bench player and between 2008 and 2012 he wasn't even picked for the national team at all in any capacity. Its only after consistent performances under Conte did he become a first team player for the Azzuri.
Wat?! Barzagli was starting CB for Wolfsburg, missed very few games during his time there. In any case most CBs peak at 30es.
I dont think I should say anything about Bonucci. Unless you were blind you should know that he was a terrible defender and it took Conte a lot of time to get anything out of him.
Actually this has been Bonucci's best season, so credit goes to Allegri. In the previous few years one blunder per game was his standard contribution.
Your judgment of the squad is completely based on retrospect rather than on the context back then. Its as wrong as saying that Buffon and Casillas are not great goal keepers because of their current form while ignoring their past. Milan's players were established, experienced and were already champions before under the same coach. They had no players that needed to rediscover themselves, they had no youngsters that never had a top level season yet, they didnt get a new coach, they didnt add multiple new players to their squad the way we did, they had an on fire Ibra that was one of the best 5 players in the world. They had the best defender in the world.
Milan had old, decaying team, although some classy individuals like Ibra and TS, mediocre bench (unless you rated players like Aquilani, Antonini Mesbah or Flamini), no young players that were expected to break through in subsequent seasons, had burden of playing in the CL, while the same core of the current team that have brought us to the semis, have also been pivotal in our scudetto triumph and in addition we had no European obligation to set us off from our path, which conicided with our lack of depth at that time. It is of no conicidence that these players still have an impact. Different coach, but players are still obtaining results. If Conte was the one responsible for them overperforming, then they'd get back to being mediocre this season, when according to many (especially you), inferior manager with lack of motivational skills took the reigns. You shamelessly claimed that current Inter's team is better than our in 2011/12, and this is where the dispute arises.
The point isn't to underestimate what Conte did, as I respect(ed) his work , but I think his biggest contribution was more related to setting the right mentality to the team rather than possessing tactical astuteness, and of course to negate blatant exaggeration where he takes all the credit. This is Juventus and we'll have few rough seasons every now and then due to circumstances mostly beyond our control, but eventually we'd hire some other coach and got back on the right track. The company of this magnitude is never solely dependant on individual.
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And when Agnelli says we won the scudetto 3 years ahead of plan?
He (Agnelli) also gets the credit for that.