It's hard to say about prime and age. Towards the end of his LHW career, Jones seem to lose much of his wrestling ability. That can happen when you start wrestling in your youth and continue through your early 20s than another 10-15 years of MMA. Look at Askren. A lot of time fighters' knees and back just aren't the same by their mid-30s. Kickboxing (and other forms of striking) and grappling can both add wear, but in different ways.
The fact that Jones almost looked like his old self against Gane adds another twist. Maybe's Gane's wrestling and ground game was that bad. Or maybe the extra weight helped Jones. It's hard to say. Either way, I think a young prime Jones would easily take down Pereira and finish him with GnP (hellbows probably) or a sub. It's a harder call now.