The amount of money that Juve have paid/are paying for Chiesa was and still is outside Milan's limitations.Even his form of last season at Juve, he was far better player than Casti. It's just Juve preferring Chiesa and Kulusevski over him. My biggest regret is, not purchasing Chiesa last year, what a monster he has become.
I'm not convinced Bernardeschi is far better than Casti (based on last season). Stats are not everything (as noted with Alexis) but Berna played 27 times in Serie A last season, scored no goals and got 3 assists. In fact he did not score a goal in any competition. Samu got one goal and one assist in 28 appearances in Serie A. In the Europa, 2 goals and 2 assists in 10 appearances.
IMO, replacing one with the one would be reminiscent with the deadwood revolving door policy that we witnessed in recent years.