I think it was a smart move by Brooks. I
don't think he was trying to send a message, I think he was trying to win. Westbrook was shooting decent from the field but had committed a turnover and forced shot that resulted in a miss on his previous 2 possessions. Brooks clipped Westbrook's cape before he had a chance to *try* to go into hero mode. It benefited his ball club. I would have rather seen Westbrook in trying to save the day and giving up the ball and forcing shots.
Even if Brooks was sending a message, it was brilliant. If anything, it tells Westbrook he doesn't have to be on the floor in crunch for his team to flourish. It should have been humbling and opened his eyes to a new avenue of winning. That's actually the last thing Dallas needs. Westbrook maturing during the series and not after from his couch. I think Dallas is in trouble if Westbrook stops playing so selfishly.