I think the mistake was more in keeping Brown too long, far after his value had clearly dwindled down to nothing. He once could have been a key piece of a significant trade a couple years ago, but at this point one would think there's more upside in keeping him than trading him (plus a pick) for a player whose equivalent could have been signed in free agency.
I think the prevailing take on Brown, is that he'll never be more than a tweener. Not prolific enough offensively to be a true top 6 guy, and doesn't bring anything else to the table. He has great size but doesn't use it to his advantage, struggles to play the game with enough pace and has been quite injury prone.