Tatum posting up is nice against smaller defenders, but I doubt the efficiency holds up against bigger ones. I know he's stronger this season, but I don't think he's ever going to have the lower body strength to dislodge a similarly strong/lengthy player.
One good thing is that, as opposed to driving, posting up is slower and more methodical and seems to be a rhythm Tatum is more comfortable with. It also makes protecting the ball against swipes easier, which is something he has a problem with. The reads on where a double is coming from and who to pass to would seem to be easier as well, as opposed to driving into a thicket of defenders that are trying to draw charges, swipe at you, or stunt and trick you into throwing it away (or also throw it away yourself which Brown and Tatum do all the time due to wonky handles).
Anyway, I like it in certain instances but I'm still skeptical that it'll be a cure-all. I don't think this is going to be as productive as when LeBron started posting up since he's actually built like a PF of olden days and is an amazing passer. I could see Tatum eventually mastering the fadeaway jumper out of the post though, in the same way that Jordan made that an unguardable shot. Actually physically moving a guy and comfortably getting a shot though, I don't know. Watching some of his post-ups, he kind of gets the ball up there and it bounces in, but it's not like he got off a totally unbothered shot. Sometimes those are going to roll out and the percentage will go down.