Gehrman varies up his attack timings more and the Dark Souls 1 parry window is still pretty big, so even with parrying Gwyn is easier. Plus, you can't block into an easy parry like you can with Gwyn.The parry in BB is easy and feels safer than DS so I guess that make Gehrman easier
Gehrman's designed around parrying, even if he's still too easy with it. Gwyn is a complete joke the moment you parry him once because he literally will only do one attack on wakeup IIRC.