Tatum hasn't exactly been setting the world on fire, but Brown has been much worse this year.
These are Brown's splits
41.9% 2PT, 27.7% 3PT, 62.1% FT, 11.7 ppg, 4.5 rpg, 1.4 apg, 0.5 spg, 0.5 bpg, 1.2 tpg, 2.7 fpg
Those are all significantly worse then last year and while 11 games isn't a season, it is starting to be a large enough sample size that concern should be setting in for everyone.
While Tatum's shooting splits are worse, he is actually scoring more, rebounding more, and getting more assists then he was last year. So he is at least being active and trying. I have far more confidence that Tatum's shot is going to fall then I do in Brown turning it around. Brown just looks lost and out of place out there most of the time.