I think that team would have been capable of winning a championship. That Boston team would be a near ideal roster make up for AD. It wouldn't be a Davis, Lebron lets take turns situation, he'd be arguably the top member of a cohesive unit where anyone can go off on a given night in a way that's similar to Golden State.
The tragedy of Anthony Davis' career is that he's always been relegated to extremely top heavy teams. I think he's a bit miscast as a big 2-3 style player. If you put him on a team where opponents aren't constantly the box against him because who else do you need to guard, he could be an absolute menace scoring in the in-between moments of the game.
Right now he's being asked to be a high volume, Kevin Durant style iso player where he'd be better served as more of a Tim Duncan off ball juggernaut. With Kyrie, Tatum, Hayward, and Horford, AD could pick his spots when to dominate and let the rest of them fill in then primary scoring. Could have been a Dynasty.