Sorry, but let's not pretend that a good counter puncher can't operate in a ring ... there are lots of counter puncher boxers that move backwards, there are lots of kick boxers that do so as well. There is no reason to believe that the fight results would have been significantly different in a ring vs a cage. Diaz has to be able to first stop the runner, then when he has him stopped he has to be able to do something with it.
If Diaz couldn't keep Condit still in the cage, there's no reason to believe he could have done so in a ring, and when Diaz did get Condit up against the cage he was not able to take advantage of it, letting Condit get off the cage and taking more strikes on the break. There's no reason to believe the same thing would not have happened in a ring.
All that said, there's not much of a chance that they will ever meet in a ring, and if Diaz wants much more of a career in the cage then he better stop whining about how people have found a way to counter his style and learn to come up with a better suited cage style, or just go away.