Genbu's shield "is" better than this shield on three harsh stipulations:
.Cure pot augment is 4-5%
.Cure Casting time is 6-8%
.You've capped -50 enmity in your healing sets without using Sors
If the augment on your Genbu's doesn't fulfill even the 1st of those 3 requirements, Sors will be the best choice- unless you spend (even more) time augmenting.