I think this debate is interesting. I am not sure the answer. I go more on what I see on the court first and stats more as a secondary consideration. Both matter. Both should be considered.
Last season, Brown was +9.9 per 100 possessions. Tatum was 12.0, White was 11.7, and RWill was 10.4, the only regulars with higher numbers. I can't look at that and conclude that White is better than Brown, based on what I see on the court. But I do look at these numbers and conclude that all of these players are valuable and impacting winning. That is the quantitative part.
Qualitatively, when I see Brown play, I see a top 25 player (seems to be agreement on that) and I see a player that is offensively inefficient, even kind of sloppy with the ball at time, but a player that helps the team win.
Brown does seem to play a lot when Tatum is out. Checking the numbers on this, Brown has 438 minutes this season with Tatum (+15) and 139 minutes without Tatum (+13). Tatum without Brown, +83 in 198 minutes. This is for this season. Seems to support the premise that they are not good together. Last season though, the best combination was when both were on the court (+454 in 1425 min). They were just fine together and actually good when only one of them. Just Brown, +25 in 610 min and just Tatum +247 in 1064 min. Much better with just Tatum than just Brown.
Now I don't know if Brown is playing more with lesser players than Tatum as was suggested in a post above. I can't think of a way to sort for that. Subjectively, it seems that when it is one or the other, the other 4 players on the court are about the same.
What does all this mean? To me it still means that I think Brown is an all star level player and I think he fits just fine next to Tatum. I would rather have an all star big who can score 25 pts next to Tatum but I fine with an all star SG in Brown.