This is not the first time that Brown has been put out there as the #1 or the main guy or whatever you want to call it. There are periods in pretty much every game where he is out there and Tatum is not, and there are games that Tatum has missed. So far this season, I would say that Brown is not playing as well as he has in the past in the same situation. He is scoring very well, rebounding enough, but he has high turnovers. I don't really like assists as a stat as many times it is not just one good pass that leads to a good look, it can be creating gravity and then a couple of passes. That said, as explained above, it seems he is making good passes, creating opportunities.
I think there are two issues at play, I don't think he is 100%, he does not look quite the same to me. Nothing serious, just a little out of rhythm, out of sync. The other issue is that he is trying to facilitate a much weaker team than he has had the last few seasons. The surrounding talent is not nearly as good and the group is not as familiar playing as a team together.
None of this is really a surprise. Brown is one of the best #2s in the league, but being the #1 on a not so great team is something different. Didn't everyone expect him to have struggles with this role at times, especially at the start of the season, coming off an injury? Next season Tatum will be back and Brown can be a #2 again. None of his struggles trying to be a #1 on a bad team are going to matter. It doesn't mean we should trade him for draft picks.