Hmmm,
Vidal 87,8%
Pirlo 86,6 %
Marchisio 84,1 %
Pogba 83,6 %
I somehow doubt that Vidal is a better passer than Pirlo.
About Mirko's bad passing statistics, I think the answer lies in his through ball attempts. When successful, those attempts end with a 100% chance. Mirko tries them a lot and he's in serie A's top 5 in regards to accurate through balls. Ahead of him are only Totti, Pirlo, Hamsik and Cassano. He has as many accurate through balls as all the other Juve attackers put together. In short, he tries those a lot, and naturally it ends up with many lost balls.
Take Totti for example. His pass accuracy is 73,9%, which according to you is very bad, right? But he's a brilliant passer and he tries lots of difficult passes, just like Mirko. But Totti is a master of those difficult passes, and even if many of those don't work, he's the best "through ball" passer and regarded as a top passer. Cassano is a similar case. Pass success is only 72,2%, but you can't say that he's not a master passer.