Seems like you yourself are basing this too much on Overeems K-1 background.
If and when the fight between JDS and Overeem happens, I see JDS being clearly the favorite.
Overeem may have been the K-1 grand prix winner, however they compete in MMA. JDS is training wrestling and BJJ with the Nogueiras and other Brazilians, and I believe he will have an advantage over Overeem in that despite the size and strenght advantage
It's not like Overeem is a rookie MMA fighter here with just a striking background. If you're heading that direction, you have to give the advantage here to Overeem who has 19 SUB victories and has proven himself in submission grappling.
In terms of striking, Overeem is not the best in K-1 even if he won the grand prix. JDS is considered the best striker in UFC by boxers like Klitschko and David Haye.
Like you said, it's an MMA fight. Whether someone considers them the best or not in their respective worlds won't affect the outcome.
Going by the logic that JDS only uses his hands and kickboxing is better then boxing, then a top k-1 fighter like Mirko Cro Cop should have beat JDS by striking, but he got stopped.
Also note that Overeem has a suspect chin, and was rocked fighting in K-1 by people no bigger then JDS.
Logically, kickboxing is better for MMA than just boxing but it's really a matter of utilizing it and putting everything together. Your kind of using MMA math here which never works. Just because Mirko couldn't do it doesn't mean Overeem can't either.
Just because JDS never competed in K-1, doesn't mean he's not a top striker that can't beat Overeem in MMA
That i agree with, JDS is by far one of the best strikers in the division and can knock out anyone with one punch. JDS is going to be Overeems toughest test to date.