They should have had a younger actor for earlier scenes. The last 2 hours (from when they have the ceremony in Frank’s honour), keep De Niro (that’s where the shades of legendary De Niro get to shine).

I personally didn’t mind the deaging and loved the movie, but it has proven to be a big point of contention, especially on De Niro who has the most time period changes in the story. Get a younger dude for the earlier era (hell, give it to Bobby Cannavale and get another dude for Cannavale role) and then let De Niro enter for the last 90+ minutes.