I believe all of you here deserve to know the suffering of Mavericks fans: Wesley Matthews makes over 17 million dollars a year and plays absolutely horribly. I believe he is currently the worst starter in the league.
Right now, Wesley Matthews is averaging 12/3.1/2.4. At first glance, that is not terrible, especially since he had a reputation of being a 3 and D guy. However, his shooting splits are truly awful. Thus far he is averaging 29.2/25.4/90 on his shooting, a far cry from his 39.4% field goal percentage in Portland. And sometimes percentages don't speak to us, but he is 16/63. He is taking 8 threes a game and is missing 6 a game! Those splits give him a true shooting percentage of 41.8%, that makes him 4th lowest among players with at least 70 points out of over a hundred players. Thanks to that horrendous shooting, he has an offensive box plus minus of -3.4
"But, isn't he known for his defense??" Yes he was. Except now his defensive box plus minus is a 0.2, just barely at league average. His defensive rating sits at a 108, which is also not good. However, those two stats don't take into account his offensive numbers. When you add in offensive numbers, Wesley Matthews now has a BPM of -3.2, which is very bad. His net rating is also a -20 thanks to an offensive rating of 88.
Lastly, his on court vs. off cours plus minus. Last year with the Mavericks Matthews had an on court +/- of 2.0, so far this year he is at -7.2. His on/off has also decreased by 7.7 points, which is incredible in its own right.
TLDR: Wesley Matthews is awful. His PER is 7, his true shooting percentage is one of the worst in the league, his net rating is -20, and his defense is no longer good. Somehow a contract signed before the cap spikes is one of the worst contracts in the league.