There's more to offense than scoring points. There is a stat called Offensive Rating which takes into consideration things like points, assists, turnovers, and possessions used up. Here's the teams for this year, from
http://www.barttorvik.com/#
Aaron Jordan 114.1
Tevian Jones 110.1
Da'Monte Williams 105.1
Trent Frazier 104.5
Andres Feliz 103.7
Ayo Dosunmu 103.5
Kipper Nichols 99
Giorgi Bezhanishvili 98.7
Alan Griffin 87.8
Samba Kane 87.3
Adonis De La Rosa 84.7
Tyler Underwood 68.4
Samson Oladimeji 65.2
Drew Cayce 40.8
Zach Griffith 22.9
When you take into consideration everything involved in an offense, Williams is one of our best offensive players. That is why he plays - because the coaching staff doesn't just look at points score and pretend that is the entire story.
The issue with Williams' game is his usage, the rate of possessions finished up by his actions. It is by far the lowest on the team. It is actually lower than noted blackhole Jalen Tate's was two years ago. That is not necessarily a bad thing. Williams is lower than Tate because Williams doesn't use up possessions turning the ball over while Tate's TO% was very high. Williams will often look to make the pass that leads to the pass that leads to the bucket. On one hand, that is selfless basketball and is good. On the other, if you have a shot you need to take the shot because a shot in hand is worth two in the bush.
Williams is a good offensive player who is not aggressive enough. He improved his 3 point shooting from last year and got a little more aggressive. I think that trend will continue. Coupled with his excellent defense, I think he will fill AJ's role and then some next year.