He's probably been reading Flight Journal. They did a piece a year or two ago, ostensibly applying a range of criteria to determine the most successful fighter of World War 2, and I'm pretty sure the P47 came out on top. I'll try to remember to dig out the issue when I get home...
Of course it all depends what you mean by 'better', which all depends on the relative weightings you choose to give to factors like:
range
firepower
handling
manoeuvrability
high level performance
low level performance
climb rate
diving speed
survivability
versatility
pilot comfort and visibility
maintainability
combat record
years in service
Certainly the P47 scores pretty highly in most of these categories, but your thinking on whether the P51 or the P47 is better simply depends on the weightings you choose to apply. For example, some might argue that any liquid cooled fighter is fatally flawed on survivability alone...
Or you might just decide that the P51 looks and sounds better...
