He is a better MMA fighter, but if you think Cain would beat Junior in a boxing or even kickboxing match then you are literally so dumb. Like, there is literally no way his striking is actually better. What do you think he's gonna do, flash the same 1-2 over and over...?
It's easy to claim someone is a better striker based on "oh, they were dropped!" but if you actually look at what makes up their striking games, Junior has his own game while Cain's game consists of kicks with 0 set-up or head movement (and he does get clocked while standing bolt upright in front of people a good bit, see the Rothwell fight), and a 1-2 which literally only exists to set-up takedowns.