Bas Rutten felt like coming out and saying a few things which essentially amounted to: Junior Dos Santos will defeat Alistiar Overeem because Overeem has a glass jaw.
Everyone is entitled to their own opinion and an awesome guy like Bas Rutten has certainly earned his, but as Obi-Wan Kenobi would say..."Only the Sith deal in absolutes", and in my opinion the fight simply isn't THAT easy to predict.
First off, I'm a fan of both guys, So I don't "Have a dog in this fight" like a certain Mel Gibson might try to say.
Either guy can win. Junior Dos Santos knocks almost everyone out. He's been to a decision twice in the UFC, and in both fights he rocked his opponents severely. He is simply a knockout artist and has massive power in his hands. Alistair Overeem being knocked out by him wouldn't mean Alistair sucks or that he has no chin, because JDS can knock practically anyone out.
But on to that point itself:
Alistair Overeem has no chin - Bas says this is the case because he's taken a lot of damage and has been TKOd/KO'd more than a few times. He's suffered 6 losses by knockout or TKO and 1 was a submission to strikes.
A few things are commonly believed about knockouts. Once you get one, it's easier to suffer another, and the easiest time to get knocked out again is close to the previous knockout. Alistair Overeem suffered 4 of these TKO/strike oriented losses in 14 months. It's safe to say he was taking too many shots and his chin couldn't recover. On top of that, he was taking a lot of fights and arguably overtraining in general...then throw in the fact that he was stil depleting himself to fight at 205 during some of this time. But I think it's also crazy to consider that even when he was suffering these onslaughts...I'm not sure if he was over actually seperated from consciousness and out cold on the canvas. He always seemed heavily rocked and dazed...but still awake.
Another popular line of thought with knockouts is that the longer it's been since your last KO, the better it is for your chin to recover a bit. I believe we've seen a little bit of that with Rodrigo Nogueira. His chin looked completely shot against Mir, seemed back to form against Couture, was blasted again by Velasquez...but after well over a year out, was able to take a few solid shots from Schaub without any real problem.
As far as MMA competition goes, Alistair Overeem has not suffered a knockout or even been rocked since September of 2007...that's nearly 4 and a half years. However, in kickboxing, it hasn't gone as easy. He seemed to be 'dropped' in March of 2009 by Bonjasky, although some contest it as more of a slip. He suffered the '2 knockdowns' from Hari in December of 09 that earned him a TKO loss.
He was rocked in those fights but not formally TKO'd...but even if you want to include that, then Alistair hasn't lost by a form of TKO in ANY fight in over 2 years. He was caught right on the chin with a straight left form Tyrone Spong that Spong literally thrust his whole body into....and that visibly stunned Overeem, but Reem covered up and showed a good ability to keep his composure and was never knocked down. That was December of 2010.
But basically, the damage he has taken in the last 4.5 years is minimal compared to the damage he took in the 2 years before that. If chins do recover...then his has had a pretty good grace period to do so.
Another reason I think Ubereem is able to take a punch better than regular 205 Reem is the fact that he is now muscled up. I'm referring specifically to his neck muscles. They say that beefed up neck muscles can help you take a punch better because it keeps your head/chin from moving as much when you take a big shot.
I mean...to me, between EVERYTHING, the depletion to 205, overtraining, and consecutive damage Overeem took from August of 05 to September of 07...to the fact that he has shown a better ability to take a punch with his uber-neck, to the fact that the last 4.5 years have seen him take far far less damage than those 2....to me, it's all pretty convincing.
I don't believe Alistiar Overeem has the best chin at heavyweight, I wouldn't even say he has one of the best...but in my opinion, he is far from having a 'glass jaw' or 'no chin'