JDS is a better striker by far...
The issue here is that that fact doesn't really matter in the big picture in MMA or specifically in comparison of these two fighters or how they match up.
JDS has crisper technique than Cain, faster hands, more power in his hands and is more plodding in his footwork and doesn't throw many kicks (but I suspect this is for balance reasonings/TDD)
Cain's punches are usually more the type of looping shots, he tends to be a little sloppy at times, has good power but not great power, mixes up kicks every once in a while, kicks are average for a heavyweight in terms of crispness and power, his movement isn't very balanced or necessarily even quick, but he is a tad faster than JDS is in terms of footwork.
In terms to how their standup works in actual functioning relation to when they fight... The reason Cain got knocked out the first time was because he isn't as crisp with his punches as Junior is. He threw his hands and was a little sloppy and Junior went right over the top and smashed him. That's a sign of Junior's technical superiority. Both men were fresh, Junior won.
In the second fight, from the milisecond that fight started, Cain used an amazing pace to wear Junior out. Junior gassed and with it, all of his skills and power were diminished due to the fact that he just couldn't breathe and then Cain hit him with the punch that hurt him and essentially ended the fight.
So yes, Junior has better standup, but Junior can't use that advantage if he's winded and Cain is going like a maddawg with his cardio. Cain fought really well in their 2nd fight, and tbh, he should fight almost everybody like that... There is no equal in terms of his pace, and a tired man is a beaten man, no matter how skilled or powerful they are.