DMI is ignored, largely.
To judge how good a player is you're better off looking at his average game rating, or failing that his salary. However beware that young players (18-23) may be better than their salary suggest, especially as the season goes on.
Looking at game rating is an excellent way to determine how good a player is. The bigger pool the better, so you're better off looking at player's average game rating from season 7 where possible. This is the best indicator there is to how "good" a player is, assuming the GM isn't playing them out of position, or for too many or too few minutes per game. What level is "good" depends entirely on what league you're playing in. 6.0 is good in some leagues and anything below 9.0 is very poor in higher ones.
Salary figure is your next stop. There is a formula which determines a player's salary from their skill points (it's a complex formula i should imagine, based on position related to skills, and age) and this is re-calculated at the start of every season. The higher the player's skills for their position the higher their salary. So the salary figure is a much better indicator as to how good a player is than DMI.
So, in brief, if you're looking at a team and you want to see who their "best" players are, click their roster page then sort by salary.