Whitts has never been blessed with pace, so he's hardly lost that has he's aged. What's different between now and when he was at his so-called 'peak', is the players he's playing with. As has been said above, he's got no willing runners and no-one to pick out a through ball with. He's probably been involved in more goals than any other player this season (either scoring or assisting) and can pick out passes that the rest of our midfield can't even see.
Joe Ralls is a decent player, but he is not Peter Whittingham. He will take at least 2, more often than not 3 touches before playing a pass.
It's the usual Cardiff fans being unable to appreciate someone not running around a lot, unfortunately.