Just think he's limited. Don't get me wrong, I'm not one that declares everyone crap or great. But he's not particularly pacey, nor is he great in the air. He's fine. I just don't see the upside. He doesn't strike me as particularly athletic. His foot skills are fine, okay distribution. He just does nothing outstanding. I like that he's aggressive and tough.
Keane is much better in the air, seems more athletic, and obviously has the length to be one of the best CB in England.
Just don't see Gibson having that kind of upside. I can kind of see how he could be more of the ball winner in front of Keane, but not sure he's better than Williams, nor do I envision him ever going to be.