Well those pictures are a bit deceptive IMHO.
The one with Edgar clearly has Frankie standing on his tippie-toes so he doesn't look like a hobbit in the staredown. Frankie is 5'6", a good 3 inches shorter than BJ. If you watch the fight again the size difference is much more apparent than in the staredown.
Kenny again looks waaaay leaner and weaker than BJ at LW, and I'm convinced he'll look terrible at FW. This is a guy who fought at MW in TUF. My discussion wasn't about whether it's possible to cut infinitely, but whether it's beneficial to performance at all or actually makes one a worse fighter. I'm sure Kenny will prove my point by getting his ass handed to him by Aldo/Mendes etc. and moving back soon.
The only one of the 3 who's actually bigger is Diego, who was probably the biggest LW in the division bar none. But he was cutting far too much weight and his performance obviously suffered a lot IMO. I'll give you though, if a guy like that can cut to LW then theoretically BJ can make FW. It's just BJ would make a terrible FW. He already had cardio issues at LW, I think he'd gas in 1 rd after as hard a cut as the likes of Diego and Anthony Johnson go through.