J will probably turn out like a bit of a griseled old Centurian....reliable in the thick of a battle and will keep going but not a great tactician and the younger ones will get away from him.... ...but if you're in a battle you gotta have a reliable old soldier in there!
It's easy to say this and that from the stands, but the people who work with him every day think he's fit enough to do a job. As for slow, yes he is, but are many centre halves really that quick? I'd say most of them get to where they are by reading the game well and using their physical prowess to good effect. Jaidi does these very well. My worry is more that he's not the fittest and he tends to get sloppy when he's tired rather than his ability to cope with Championship strikers.
I would add that the pairing of him and Fonte has been exceptionally good. Fonte kind of acting as a sweeper works well when the two are playing.