I don't agree. Take young Ned's example.
The fact that they used a younger actor felt more natural than it would have had they used scruffy old Sean Bean to portray 20 years younger Ned.
When you go back two decades, it is natural that the audience will expect change. Using Sean Bean in the Tower of Joy scene would have made it look like it happened 5 mins ago, just like it felt with the Mad King scene.
The direction can be so lazy at times that if Ned was still alive, they would have used Sean Bean in the Tower of Joy scene.
You can disagree as much as you want, but I would insist that they should have either given Jamie a makeover/different hairstyle or used a different actor, because using the present day Jamie in the flashback scene simply did not feel natural and did not show that it happened a long time ago, just like it felt in the Tower of Joy scene with a young guy portraying Ned, where you could instantly appreciate the time span.