He doesn't project to do anything at an NBA level when he enters the league other than finishing in transition.
He may be able to do other things, but there's no way of saying for sure what those things are.
Alright, I'll bite.
The dirty little secret is that Brown was better at finishing at the rim than Simmons in college. Simmons had 82 unassisted makes at the rim. Brown had 71. But on those shots, Simmons, with all his athleticism, only converted 54% of the time, while Brown converted 62% of the time. And that was with Cal's clogged floors. LSU's were more open. Simmons had an unreal 77% free throw rate (ft/fg), but Brown was impressive in his own right at 58%. For reference, Justise Winslow had a 44% free throw rate.
All while Cal played at a paltry rating of 68 for pace, while LSU had 73. This shows that Simmons had more open court opportunities than Brown did.
Brown actually "projects" to be a better driver at the NBA level than Simmons.
Combine that with comfort and a developing consistency from the outside, and Brown might be a better scorer than Simmons at the NBA level.
It's not like Brown is a slouch at passing either (2 apg). Simmons is clearly superior in that regard, but Brown is not going to be a score-only guy. He has high IQ and good court vision. With an open court and better teammate shooting, it's not hard to "project" Brown as a good passer on the wing.
There is also reason to believe he "projects" to be a solid defender immediately. He had a 3.3 DBPM and also one of the highest defensive ratings on his team, meaning his team was significantly better defensively with him on the court. This shows that he knows how to help his team play good defense, and if you combine that with his elite athleticism, he "projects" to be a solid defender immediately.
Driving. Passing. Defense. He projects to do all at least above average level immediately in the NBA.