Well, guess what guys?
This is a big thanks to everyone pointing out the whole GCD concept.
Due to your adamant passion regarding the whole GCD concept (which quite honestly I’d never paid any attention to) I’ve changed my approach somewhat when playing Disc–notably when no movement is currently or shortly expected to be needed. Casting Shadow Mend is, in these cases, and when health bars are not at full better than PW:Shield, and that is related to GCDs. I am hence casting more Shadow Mends vs PW:S than before due to this awareness. And it has upped my game. (Not when movement is in progress, needed or expected though, but that is beside the point).
So there you go.
Thanks again.