You must be new to mma or have a mild case of down syndrome. A professional kickboxer will destroy a boxer every time. In terms of striking, Boxing is first, then Kickboxing, and mma is at the bottom. Alistair isn't the best technical striker, but better than any other other heavyweight, though we have to wait for the JDS fight to see who comes on top.
I don't know if you've watched any K-1, but there have been pro boxers in K-1 and they haven't faired very well. When they start getting kicked everything changes. The cute little footwork goes to shit after a couple of proper K-1, Bonjasky-style mule kicks to the thighs. Nevermind a head kick. I've seen JDS make a lot of mistakes leaving himself open in standup exchanges. Overeem, needless to say, is stronger and probably hits as hard as Carwin, if not harder seeing as he is more techical.
Regardless of what happens, this is going to be a hell of a fight. Junior probably has a better chin than Overeem since he's never been k'od, but Overeem has the power advantage. If in doubt, while JDS couldn't knock out Big Country, Overeem put down Ben Edwards (look it up to know what this is a valid comparison) three times from three punches in one round.
Wait, there is a contradiction there. You first state that a kickboxer would destroy a boxer, and then claim that when it comes to striking, boxing is first, then kickboxing and then MMA is at the bottom. Are you sure you don't suffer from Down's Syndrome

And yeah, boxers have lost in K-1
fighting with K-1 rules. Have you seen the glove size in K-1? Almost as big boxing gloves. In MMA, the gloves are much smaller and you can knock out someone with one well placed punch.
As for Overeem having more power, yeah, that's why he wins with devastating KOs, right? I mean, he couldn't KO tire-repairman, Brett Rogers, nor could he knock out Werdum even though he lended two solid blows to Werdum in their fight. Now look at what JDS did to Werdum in their fight: one uppercut and Werdum went to sleep. Overeem wins most of his fights via TKO or submission(guillotine chokes) and not KO. The guy has so little power for his size. He can't bust a grape!
A great boxer beats a great kickboxer in a fight with tiny gloves 9 out of 10 times. A great boxer is better with his fists than a great kickboxer. It is much easier to KO someone with a right overhand or even a well placed jab to the chin than with knees. Great boxers are very good at eluding the clinch with their foot work and they are very good at the clinch.
I predict JDS will knock out Overeem because he has more KO power, a tougher chin, and because I can see JDS connecting with his hands much faster and easier than Overeem being able to successfully clinch and knee JDS. Boxers are very good on the clinch. Getting out of the clinch is such a huge part of boxing. Yes, Overeem is stronger and if he clinches JDS might not be able to get out and get KOd. But I think that if Overeem gets that close he will get an overhand right to his ear before he gets the chance to do that.
SUCKMYMUSCLE