DMI could give you indications on the progress and/or form of your opponents players.
There are ofcourse plenty of ways to compare and prepare for games.
I find Gamereports, Salary and Gameshape/DMI useful .
Most important are gamereports, but they take the most time to read too. Sometimes you even need to dive into play-by-play to find out defensive matchups and other stuff.
Salary is an "easy" way to rank/compare your opponents players, somewhat accurate for all players in the beginning of the season and less for training/old(33+). Multitalented players have lower salary than their contribution on the court and this could be "found" in the gamereports. Older players drop in skill during the season but keep their salary through the season. Training increases skills but salary remain the same. Gameshape/DMI could help you track this over time.
Notes:
Some players perform better/worst in certain tactics.
Against bad opponents your players get better ratings.
So don't look too much on DMI, trust the Gamereports more.