I think people are throwing Overeem out of the picture a bit too early.
He was quite easily defeating Bigfoot the first two rounds, more than once he tossed Bigfoot out of the way/down like a child, he didn't even look like he was trying in that fight. He got really cocky and paid for it, but I highly doubt he will do the same against JDS.
Overeem can definitely beat JDS if he plays it smart and is in top form.
But Silva is slow, has not a good striking technique and stood right in front of Overeem, that's something Dos Santos is not and won't do. Before the Silva fight, I thought Overeem could have a reasonable good chance to beat Dos Santos with his kickboxing, but after the first round I thought otherwise and gave Overeem a much much smaller chance to win against Dos Santos (he was cocky and dominant, but still couldn't really hurt Silva)