Perhaps he is just very sure that Pro is a better game.
Perhaps I'm a fanboy too, I will argue to the end that I think Pro is a better game, if someone wants to make their case otherwise. I've read 1001 reviews that conflict with my own, but I tend to see reviews as rough guidelines about the game, to truly judge it you have to play both and decide for yourself.
I tried Fifa a fair few times, used to love it before I migrated to Pro, can't even play the game without feeling uneasy now, it's just not the same and I'll be damned if I let a review decide how I feel about a game. To even compare the two, you have to play both, a review is not equal to that experience in anyway possible.
I still don't see why people care though, if I like Pro, or Fifa, what does it matter to anyone else? Sure, Fifa could be a much better game, to someone else, but for me it isn't, and someone telling me otherwise will not change that, and neither do I expect to change minds either. It's a very petty disagreement to have, one that people tend to take far too seriously.