Tatum I see something people are going to hate to see my type but his game feels very Anthony like on the offense end. Will be able to score from any angle any direction in multi of ways but he is without a doubt looking for his with tunnel vision. I think Brad's offense keeps him honest for now but in the future I suspect he will look to get his outside of the set offense.
I guess we're going to find out, but I don't see the comparison, on several fronts.
For one thing, in his rookie year, JT is scoring more efficiently than Carmelo ever did
at any point in his career. JT has a TS% of 59, which is borderline elite. Carmelo's career average is 54% - a hair under league average - and in his very best season was under 57%. This year he's at a putrid 50%.
One reason JT is more efficient is that he doesn't take a lot of bad, me-first shots. Carmelo has never, even in his rookie year, averaged fewer than 15 shot attempts/game. His career average is 19 FGA/game on a usage rate above 30%(!). Tatum is averaging 10 shots/game, on a usage rate just under 20. He's far from a black hole.
Maybe Tatum's annual numbers are lower because he was surrounded for most of the year by vets and deferred. A bit. But even when the vets went out with injuries in March, his usage only went up to 23% - and we hear people clamoring for him to take more shots because his efficiency hasn't suffered. All this tells me he has much better judgment about when to shoot, and may even be a little gun shy. I see nothing that tells me he won't accept coaching.
Maybe your main point is that he'll never become a great playmaker. That's harder to quantify. We'll see; he wasn't asked to do much in that area at the start of the year. But I've seen increasing evidence that as they're unlocking him in the pick and roll and getting more touches he's starting to make plays. I've seen some very nice passes over the past month.
The last thing is that comparing a player to Carmelo raises the specter of selfish play and no-defense. Even if you didn't intend this, that's in the package. I just don't see anything in Tatum that looks that way.