Thats the thing though, what top jump horses could have run 5th in an Arc as a 3yo? average handicappers(70s 80s) on the flat are more likely to improve for the jumps, the listed/group horses on the flat at 3yo and 4yo rarely match their flat form never mind improve for the jumps.
Hurricane Fly is the only one I can think of but even he wouldnt have been good enough to run in the Arc as a 3yo. Jump horses should still be babys at 5yo and peak at 7/8, they shouldnt be starting at 5yo with a full high level flat career behind them.