If they finished at the fourth position then they could have at least kept their consistency. But it is ruined also. I don't know what the new board are thinking about Allegri now. I would have already sacked him because of the poor look in most part of the season. Allegri's system isn't good anymore. Juventus should be able to create more goal chances than this. Even Vlahovic couldn't become very effective like in the last season due to this.
If not get 10 points deduction Juventus has chance for finishing on top fourth standings placed and participants in Champion League next season, but fatal mistake with not transparent and manipulative about transfer values made FIGC have deduction 10 points for Juventus. Indeed points deduction, Juventus faced many problem in this season with Allegri tactic more boring and he can't make Juventus play attractive for scoring many goals on every games.
Dušan Vlahović has consistent performance with previous club Fiorentina, but under Allegri he faced difficult keep scoring goals on every games and I don't think wrong with Dušan Vlahović but how difficult for understanding with Allegri's scheme.
All that has passed now, take this punishment as a reminder that they will not do the same in the future because of course this will only hurt themselves in the end.
The opportunity to be in the Champions League just slipped away, they also could only be in the Conference league next season and that was unimaginable before for a club like Juventus.
Talking about Dusan is indeed a bit complicated. His decline was very pronounced and indeed as you said it looks like Dusan has indeed lost momentum at Juventus and he failed to adapt to Allegri's scheme.
On the other hand, he is also rarely able to get the ball very well for himself which makes it a bit difficult for Dusan as he is always a bit of a good supply when it comes to the ball. Injuries also took a toll on him in this regard which made it even more difficult for Dusan this season.
Now some news that he is interested in several big clubs are still being heard but indeed there is still no development whatsoever regarding this matter. Now he also has to try even harder because his potential is still very good and it would be a shame if his potential which had been honed at Fiorentina had to be destroyed at Juventus.