Per wiki:
Ronaldo: 57 app, 34 goals: Goal every 1.67 matches
Dybala: 196 app, 83 goals: Goal every 2.36 matches
Ronaldo so far has carried more weight in his short amount than Dybala has in that same amount of time IMO of any amount of his time here.
Per your point you're trying to make: in the last 4-5 years I would put my money on Buffon/Chiellini or most of our CBs that have been here that long
Buffon had that record breaking run of zero goals conceded like 974 mins or something crazy like that. I'd put my money on someone in defense.
Also, NONE of Buffon, Chiellini, Barzagli or Bonucci have completely tanked for an entire season, either. So there's that.