the point was you said when did we sign a defender that failed.
Put Jones' injuries aside, he has hardly improved since his 5-6 years or so at the club so that is a fail. He jumps into tackles, doesn't read the game as well as a top class should do.
Shaw you could argue didn't do much in his first 2 years given he was the god-send left back for the next 10 years. I'm not talking since the injury as that's a different kettle of fish.
If Darmian wasn't a fail then what was. He has hardly played and he was signed as our starting rightback and we've played Valencia nearly all season there.
We've made good purchases (Bailly) and bad ones. Simple as that.