So I went and checked out the bench stats on NBA.com. Interestingly the bench is second to last in points scored per game at 27.8. However the bench plus/minus is 9th in the league at +1.1 (I assume that's per bench player per game). That probably means that the "bench" scoring is being anchored by the starters playing with a given bench unit which makes sense given that Brad has tried to play two starters with the bench at most times. I think it also indicates that the bench is likely doing a solid job defensively.
This is an important point to think about.
Measure how good our bench is not by their scoring, but how the players within it complement one of the four 20 PPG scorers from our starting unit when they're on the floor together. Tatum in the New York game seemed to be doing a great job of not just scoring, but also passing from the top of the key to facilitate the offense with a lot of bench guys out there. This is honestly the next step for Tatum; not picking up another couple of iso moves, but learning how to see the play unfold and make a simple pass or two to get defenses moving. LeBron made a career of getting the ball at the top of the key area, attacking the paint and passing out to an open shooter. Luka is doing this now at 20 years old in Dallas. Tatum will never be the passer these guys are, but he certainly should be able to identify when a double is coming as he attacks and shift the ball to the outside.