when people take into account PPG, how often do they account for all the talent on the team, guys who deserve shots and average a lot? For instance, Heild, how many AS players did he have to take a backseat to? Kyrie avg around 25pts, Tatum 16pts, Al around 15pts, Hayward another 14, Smart about 10, and Morris about 15 (numbers probably off but not by much). How did Heild's teammate's shots and points measure up to Brown's teammates? I highly doubt his team had as many mouths to feed. Could JB score 20pts on a less talented team? We don't know atm but I don't doubt it.
I think Brown's offensive game is very similar to that of a young Andre Iguodala - strong, athletic, good size, strong finisher, capable but not standout shooter and not really a natural scorer.
if you look at Iggy's career he had long stretches of time where he was forced to be the #1 guy on some not-overly-strong Philly teams, and yet he only averaged 19 PPG once, and only averaged > 18 PPG 3 times. Most of his career his ability was more like that of a 14 - 15 PPG guy, and i think you could say more or less the same for Jaylen Brown.
I think on a lottery team or highly defensive oriented team with very few scorers, Brown could peak at around the 19 PPG - 20 PPG mark with forced high usage.
If you are talking about a competitive playoff team with decent scoring depth, then I think he's more like a 16.5 PPG - 17.5 PPG guy. At least with his current play style anyway - of course players can change, and he could be a dramatically different player 2 or 3 years from now, though I don't expect that to be the case.