This is a shallow analysis. Banter doesnt need to be about a transgression or offensive at all. E.g. if you were talking to Armand Duplantis, you could tease him about how easy he makes breaking the world record look: "Hey Armand, you havent broken the world record in this past year...arent you due?"
Oh interesting. I was about to say that's not what banter means, because in my mind I always thought it's just a casual fun back and forth conversation not necessarily skirting that boundary of teasing. But then I checked the definition and teasing is a part of it. Every day you learn something new.
I think of banter as saying something offensive but not really meaning it so the humor is in being "playfully offensive" or "offensive when you don't really mean to be offensive"