I think you have to take in the fact that if a fighter has been fighting in a ring for the majority of their career any transition to a different format is going to have a massive effect.
In the case of Wanderlei he's been fighting in a ring for nigh on seven years exclusively. It may take more than one fight to make an adjustment. Yes, he has fought in a cage before, but that's nearly seven years ago. You forget things in seven years. I can hardly remember anything from some subjects I did in school seven years ago. Sure I remember some things, but I bet if I did some exams now I probably wouldn't fail but I wouldn't do aswell as I did then. Yes you can train in a cage, but I'm sure it's not the same as actually fighting someone in it for real. Especially fighting someone of the caliber as Chuck Liddel.
Fighters, like anyone, need time to adjust and gain real experience. Some fighters might need one fight, some might need three or four. Some might not even be able to make the adjustment and may not be as succesful. This doesn't make them bad fighters it just means the format doesn't suit them. It certainly shouldn't belittle what they have proven and done in the past against other people.
I own every UFC up to UFC 45 and every Pride up to the 2003 Pride MWGP. In our house we rewatch loads of fights from both. Both organisations have had great fighters and great fights going way back to before 2000. A great fight is a great fight, no matter whether it takes place in a ring, a cage or a dojo. But, if we feel like watching a whole event, we'd normally watch a Pride event. Why? Because the whole package appeals to us more. Commentators, crowd reactions to fighters and the fights, event intro's (PRIDE THEME IS THE FKIN SHIT, sorry but we love that thing), fighter entrances, ruleset, sketches and interviews. Note how none of these things are to do with an actual fighters skills in fighting. ;p