Tatum has a much better feel for the game. He's a natural, smooth player.
Jaylen is much more mechanical and deliberate.
It's been interesting to see how that has played out -- Tatum looked like a natural born star in his rookie season, but now it seems that maybe the fact that the game seems to come naturally to him has allowed him to somewhat coast and just stick with how he wants to play the game. He doesn't appear to have put in the work to change and add to his game, at least not so far. He still takes your breath away at times. He gives you the impression that he could score 30 points a game without breaking a sweat, like KD. But Jeff Green also gave that impression sometimes, as does Andrew Wiggins. Tatum is better than Green and Wiggins, but at this point it's mostly because he's a much better outside shooter. Like Green and Wiggins, he doesn't get to the line or create for others, and his defense is inconsistent.
Brown, on the other hand, has very obviously had to work extremely hard to add NBA-level skills onto his foundation of superlative athleticism. He has struggled mightily when his role has changed, but over time he works super, super hard to figure out how to find his spots and stand out in that role. Jaylen isn't a "basketball genius" like Kyrie or a natural like Tatum, but in some ways you can feel better about where he will end up because he seems to understand that kind of focus and day to day work he needs to invest in order for him to earn the kind of role and recognition that he feels he deserves.