I see no problem with the portrayal of Joffrey and would argue that its the show's best acting performance.

He can wave to crowds without caring much about it. That scene was mainly about Marg manipulating him. It also showed his naivete in that he didn't realize that crowds aren't always trying to kill him. But this experience doesn't have to alter him

His sadism has been consistent. Sometimes he's brutal about it, sometimes he's giddy

His convo with Tywin was a fantastic character builder. It showed him in a more realistic light instead of being single-minded. It's not strange for him to want some intel, want to make some decisions, and be right about some things