Offensive box plus minus has dipped each of the last four years.
Win shares per 48 has dipped each of the last four years.
VORP has dipped each of the last four years.
PER has dipped each of the last four years.
His free throw rate has dipped each of the last four years.

He can still put up some monster stats for a team, and he will still will his team singlehandedly to some high profile wins... but overall, his positive impact on winning has been diminishing and will likely continue to diminish with age, because he's so reliant on attacking the rack and on having the ball in his hands.

If I'm Milwaukee, why would I take Westbrook? I already have Giannis, who's basically Tall Westbrook with better defense. They need shooting. Why would Atlanta take Westbrook? They need shooting, they need defense, and they need the ball in Trae's hands. Westbrook wouldn't help any of those things.

I still think he's a stud 1v1 player, he's a damn bulldog, and he's shown enough adaptability that I'm not gonna call him "one-dimensional"... but I do think it's fair to wonder if his style of play has been conducive to anything other than the level of results his teams have seen. He's not terribly high on the list of players I'd use to start a team nowadays.