I don't get it to be honest.
Lang Lang and Chopin are two very different people and I imagine 2 very different performers, the latter of which we have no true evidence of, to be honest I don't know how you think they could compare as pianists xD Nevermind...
2nd, there is no need to perform in anyway other than what the music requires, and with the perfect sound, no extravagance is required at all.
So the question is why? Not just why to your question, but why do some performers seems to be more extravagant than others? It is true it can captivate some members of the audience who are susceptible to visual stunts.
For me, Lang Lang is at the top of this list in terms of living performers (I would consider him a performer rather than a pianist), you could go back a few years and see videos of Liberace doing just the same thing. Liberace was a closet homosexual so maybe there you could say will flamboyancy was in his nature, or maybe the feeling of suppression caused him to overact when it came to expressing his motion at the piano.
Lang Lang also had huge suppression as a child being forced to play the piano, his father threatening to kill himself and the Chinese culture in general is very pressured towards children. But then another thought, when we think of German classical piano we could fire out names like Beethoven, Mozart, if we think of French classical piano we have Ravel or Debussy, we could keep going on with regards to western classical music.
These generations then passed down, technique, heritage, ways of playing, performance styles.
Now when I ask you to name any equally performed Chinese classical composers who could you think of?
So now imagine this - You're a piano star, you have no heritage, nothing but purely technical finger bashing passed down from your father through endless hours of Czerny and now you need to make some money, how do you sell yourself? It has to be in the performance and this is why Lang Lang over does it.
Every other Chinese prodigy and pianist we often see are very inanimate when it comes to playing the piano because they have nothing to follow.
So going back to your question, I don't think you can do both. Lang Lang often performs very different to other pianists and it sells because it's completely different, not necessarily because it's fantastically good, he's sold an image.
Whatever you do, it has to have reason and it has to be genuine. Lang Lang doesn't fool anybody with his movements.