He didn't have to. He said that Dunk is evidence that plenty could make the step up. I disagree. Dunk is evidence that he was able to make the step up, no one else.
Every successful player in the PL is evidence that it's possible for a player to make the step up from whichever league they came from, which covers all the leagues we're looking at. It doesn't mean anything.
It would be different if you were looking at all defenders who've come from the Championship, and noted that most of them were a success (preferably with stats comparing them to purchases from other leagues, and also comparing the success rate of defenders compared to other outfield players).
Plenty is not 'all'.