Some of us have had issues with over manipulating our lips, including rolling under our bottom lip.

But there are great players, Dizzy Gillespie comes to mind, who play all sorts of ways successfully.

If someone has the range, sound quality and endurance they desire and they roll under their lip, then so be it–good for them.

I had issues where I was rolling in/under my bottom lip and the air was going down towards my feet. I had no endurance or range despite lots of practice, lessons, etc.

I have moved towards focusing on blowing straight forward and tightening the aperture from the corners and my range, endurance, sound have all improved significantly.

I consider myself a downstream player, even though my teeth meet in the middle exactly (no under or over bite). My bell still goes down a bit as I ascend, but not as much and I appear to be progressing well.

I try to think about the air column and I look at the leadpipe as I play, focusing on tightening the aperture inward from the sides inward towards the air column, rather than tilting the bell down / head back and lip under while clamping my lips down top-to-bottom.

Not sure if I’m not rolling my lip under at all anymore, but I’m primarily tightening from the aperture corners.

Hope that helps, FWIW.