Agreed. Matchups will make or break how Jon does in HW. A lot of his game works on having a height or reach advantage and that doesn't work as well against other tall guys like Stipe, Ngannou, and Werdum. Not to mention that Jones is definitely hittlable and HW power is a world apart from LHW. Jon also is strong as fuck, but would be weak compared to natural HWs like Stipe and Ngannou.
I see Stipe, Ngannou, Werdum, and Blaydes being bad matchups for him.
Cain would be 50/50 and probably be the most spectualuar fight in history. Current JDS would be tough, but Jones would probably back him to the fence and win via good gameplanning. As for Reem, at this point a MW should be able to crack him using a good gameplan.
Volkov, Struve, Hunt, etc would be fodder for him probably.