It did seem stark to me how quickly Rudiger went from solid CB option to apparently terrible in recent years.

It wasn't Frank not liking him though, mate. Don't know how anyone could dislike the guy, he's a brilliant character and was solely down to losing the solidity you mentioned.

Speaking as someone who's watched him pre and post injury at the Bridge, he returned from that major injury a completely different player. Before he was rapid, physically dominant, confident in his feet and commanded situations regularly. After it, he looked so rattled and jumpy in most defensive situations, and made error after error individually (in an admittedly poor defence). More recently, he had a couple of performances that have looked a bit more assured and calm, but I'd have backed any manager in dropping him until he regained form, as he was a liability for us for quite a while, which was really sad after some exceptional form.