While I know the point of this discussion isn't to define an ace, I think one important aspect is how deep they pitch into the game. An ace doesn't just wow you on the mound, they protect the bullpen by going 6+ more often than not. Gibson isn't quite there at 5.8 per start. Berrios is barely above 6. I still enjoy watching both pitch, of course, and this is my own made up rule just now.