You could also argue if he was that important a player, they would have kept him & gotten rid of someone else. He did play with Ronaldo at Madrid.Dybala plays a different position.
And I imagine Mandukic would be on lower wages than Higuain.
Just because they let him go, doesn't mean he's not a good player or they didn't have their reasons for doing so.
Mandzukic is also on course to match his output for Juve last season. Very sceptical about this signing because of his age and pace of the PL, but fingers crossed he hits the ground running.