I think what Tatum is doing while on a 50 win team is important because of a context you just are not going to get from looking at stats, and I really don't care how box scorey or advanced those starts are.
What Tatum is showing is that he can be an important cog on a winning team while playing winning basketball. No, not that he plays basketball for a team that wins, but plays winning basketball.
For instance, Marcus Smart has been on losing, mediocre and good teams here in Boston but always played winning basketball. Some bad stat years, both advanced and box score, but he played winning basketball. It is sort of like that old saying about p0rnography, not sure it can be completely explained what it is but you sure know it when you see it.
You just don't find a lot of 21 year olds that play winning basketball while performing at a very high production level and being a major contributor to a team that is a contender. That is unusual and hard to find.