that's the same thing everyone just loves repeating as proof of how great Chiellini is. The thing is that Chiellini has what is needed to stop a big-bodied and relatively slow player like Ibra, who relies more on overpowering his opponent than craftily moving around him - Chiellini has physical presence.
Stopping a nimble, fast and creative forwards, however, requires ability to read the game, anticipate what's gonna happen on the field and react to it before it even happened since it would be too late, otherwise ... this is why Chiellin looks so helpless, way too often, vs such players.
He is way too simplistic and one-dimensional of a player to be considered great.