It's a bit circular, this. One could equally argue that he only played behind bad packs because teams with good ones didn't choose to sign him due to, y'know, him not being that great a player.
I always get annoyed at the idea that players leave the Tigers and suddenly become amazing as I think it's largely just another stick to beat the Tigers with. But, equally, good clubs have been able to pick up reasonably decent players from us and use them in roles to which they're suited, thus getting better outcomes out of essentially the same player. Blore and Papali'i are decent current examples: they haven't suddenly become different players, it's just the Melbourne and Penrith can use the skills they have in a way that helps the team and makes them look good.
I can't help feeling that if Brooks had a lot of untapped potential he would have got better offers over the course of his career. Even in the "big four" days it's no surprise, in retrospect, that he was the one who didn't get lured away.