He has gotten better in fairly meaningful increments, each season. I think the question is how many more of these increments of improvement are we going to see? I don't think he is yet starting to approach his ceiling, he will have, what, 2, 3, 4 more seasons of improvement? He is an all star now (albeit barely), where is he going to be in 3 seasons or 4 seasons?
I think back on players like Reggie Lewis and Chauncy Billups who were raw talents to start but kept getting better for many years. I think Jaylen Brown will have a similar path and probably will be better than either. We are not going to see his peak for a few years or more for sure.
I don't understand all the treads about trading him. For Towns or Harden or someone like that? Sure, you consider it. Beals? I am not so sure and there are not too many others that I would even give it a second of thought. It is a very short list of players I would consider trading Jaylen Brown for and gets shorter as he continues to improve.