What influenced my view on the grades of Sylvia & Shield of Achilles was comparing them to other climbs of similar grades. I climbed Sylvia recently after not trying it for over 5 years and found it difficult, at least as hard as the other 22s in the quarry -The Force, Vader, Urban Ethics and Land of the Orange Druggie. The bottom crux seemed desperate – has a hold broken? A few others who have tried it recently also agree that 22 seems appropriate.
As for The Shield, I think it is not as difficult as Hang Ten (24) and I thought the crux on your 23 at Boya Quarry was harder. I also think the crux on Quarryman (22) at Stathams is as hard as anything on The Shield. Also, one of those who have led The Shield and Sylvia cleanly said that he thought there was not 3 grades difference between the climbs.
My suggested changes are merely an attempt to get consistency amongst the grades of climbs. I’ll guess we’ll see if anyone else has any comments.