[quote=OtomostheCrazy]
Well, maybe Gwyn's parry able to keep up the lore that's built around him. After having his soul burn in a flame for so long, and being reduced to a powerful hollow, maybe he just became that weak?
[/quote]
I've considered that too. Being somewhat of an anti-climax boss makes sense for him, considering he doesn't have a lord soul anymore.
Then again, Ornstein, who is both mechanics- and lore-wise weaker, is unparryable. It's just a matter of gameplay and story segregation, i suppose.