Malcolm Blight said almost exactly the same thing.
Brown's fitness has always been his biggest issue though. He's a huge man, an enormous presence, but he simply can't run the whole match. Fortunately, he's smart enough, and has been given enough freedom, to run when it's the right time to run, and he's become a fantastic player as a result.
Fitness is not a weakness of Walker's - it's one of his greatest strengths! This guy finishes training sessions the same pace he started them. He can run all day long, he just chooses not to.