It's not easy to play with a Ronaldo who desperately wants to score rather than win. However, he still has all the tools to be a top striker and I have no doubt he'd score close to what he used to at Madrid if he had the same team.
The main issue is that Juve keeps making mistakes in player recruitment. The Director of Footy (Nedved?) hasn't been successful and Juve often buys players by name (Ramsey) or form (Bernadeschi) rather than the player's actual quality or if his characteristics fit the overall vision they have for the football team.
Then they fired Allegri who was actually one of the best managers in the world in terms of tactics and reading of the game for a manager that has or used to have some sort of cult following but, in fact, never accomplished anything worth listing.
It isnt easy, but you know if you can get some service into him, he will score you goals.
Like you say, Juve are terrible with recruitment. This is such a mix and match team, no wonder they cannot get consistency.
They signed Ramsey, Rabiot on free but big wages when they have Bentencaur, Pjanic, Matuidi, Khedira.
They went and signed De Ligt when they have very good CB's and signed a younger CB too.
They traded Cancelo for Danilo and money and ended up having to play Cuardado at RB.
They have neglected to sign any wingers.