I'm not saying this is a guaranteed win for Lesnar, but he is more than just a live opponent in this fight. Before you discount Lesnar's chances, at least analyze the fight. Overeem has terrible punch defense. It's true in K1 and MMA. All Overeem does is cover up, and move away. Overeem doesn't try to set up anles. Overeem doesn't parry and counter. He just covers up and moves away, and that is against pretty much anyone he faces. If Lesnar comes out aggressive with punches, odds are Overeem will cover up and move away. If Lesnar can get him to retreat near the cage, he can shoot in for the take down. Overeem has never faced a shot like Lesnar's. I have no idea how he'll handle it. I do know that Overeem doesn't have Mir's BJJ game, and Mir couldn't stop Lesnar's ground and pound. That's not a foolproof plan for a Lesnar victory. Overeem is very big now, and may be able to stuff the shot. Overeem also has a nasty guillotine.
The Lesnar of the Couture and second Mir fights has a live chance against Overeem, for sure. Overeem has vulnerabilities. But right now, the stars are not aligned for Lesnar. He's going to get stomped. I think it's pretty raw of the UFC to hurl him back in against the world kickboxing champion on his first fight back from a serious illness. They're not giving him the chance to be at his best for a big fight. I know I've bored everyone on this forum about this countless times, but my mantra won't change: A tune-up or two is not an evil thing. It allows fighters coming off long lay-offs or illness or injuries to give fans their money's worth when they pay to see big fights. Brock is going to get horribly executed by an opponent he would have a fighting chance against if they allowed him to get back to full sharpness. JMHO.
I don't disagree with your lay off theory in general. I just don't think long lay offs severely hurt when fighters have remained active. Like Rashad Evans for example. Rashad had been out of the cage for over a year when he faced Ortiz, but Evans had only been abscent due to already scheduled fights being cancelled. Evans had been in 2 or 3 training camps prior to entering his bout with Ortiz. I think that all the gym time kept him sharp. You are spot on with Lesnar. Lesnar lost something like 20 or 60 lbs with his first surgery. I have no idea if this surgery has had the same impact. Still, to my knowledge, Lesnar has not been through as many training camps over the past 14 months as Rashad had. Lesnar deserves a tune-up.