Difficult one.
Jones fought little and didn't look very impressive in his last couple fights. Gane usually looks pretty good, but he didn't look out of this world good in his last fights either. Francis had some weight on him, but is not near the level of grappler that Jones is. People forget how good his grappling is.
I would counterargue the ring rust argument, saying that he had some time now to adapt to a HW frame. He might be around Gane's size actually.
Those two factors might about cancel each other out.
Striking wise Gane will probably have an edge. But Gane doesn't really carry that one punch KO power, which would be helpful in keeping Jon away from him to stop him from wrestling.
If I had to give a wild prediction, I would say Gane styles one round on Jon, gets an easy 10-9, round 2 Jon takes him down effortless, Gane has the illusion he would be able to snatch a heelhook or some fancy leglock, commits to that and ends up getting his guard passed easily, then gets gnpd and Jon finishes him up with a submission late into round 2.
(Don't call me out on this, this is just a bluff to look cool if it comes true)