How Brown complement Tatum isn't the question. They're both versatile wings that can do it all on both ends. As long as Tatum is on the court they're fine, and having someone of Brown's caliber is just icing on the cake.

The problem is that the Celtics were hoping that Brown could really take over when Tatum is off the court, but that hasn't been the case so far. Not always anyway, there has been bursts and in general he's still a net positive. Just not the type of net positive you need in a second star.