Team ERA is 3.76 with a 3.96 xFIP, which is a normal discrepancy. I buy Dickey (knuckleballer) and Estrada (elite changeup, high fastball that yields flies in the 'donut hole') as xFIP beaters, though not Estrada to the extent that he has. Two of probably fewer than 10 guys in the league I'd be comfortable making that claim for (Odorizzi, Wright, Ziegler, Clippard etc...). Would have said Keuchel last year too because of his defense, but contact has been harder against him this year.
I haven't seen compelling evidence that Happ should be expected to beat his xFIP going forward.