Reminding of me and my college mates arguing about tai chi and ba gua in early 1980s.
Lean or pian or yi.
Tai chi is about bu pian and bu yi. No siding and no leaning.
The truth is that you do go to one side then the other. You do lean one way or the other.
However, how do you keep your balance in transition from one side to the other.
That is tai chi all about.