Honestly, if we look in the rear window, he doesn't have any really solid wins.
Beating Aoki is good, but Aoki is Japanese so of course he has been highly overrated (this coming from a Pride fanboy). Aoki has amazing submissions but that's it. Thompson is a good win (and question is if he Gil won in their last encounter), but it's a win that doesn't warrant a top 5 ranking.
Gil is a talented fighter but based on the guys he has beat, there is NO WAY he's above top 5. If anyone states otherwise, they are incorrect, it's as simple as that.
On the other hand, I think the "who did s/he beat" rankings are worthless as an on/off-night can result in a mediocre fighter moving up the ladder ahead of better guys. Serra was rated #1 as he had amazing luck beating GSP - but we all know that Serra has never, and will never, come remotely close to being the #1 guy in a division. If I were to rank Gil based on his actual skills, which is the ONLY way you can rank him above #5, I'd still say he falls in the #5-10 range. He looks good, but he doesn't look like a top 5 guy in my opinion.