Yeah there's always going to be grey areas and different builds in dueling gear. That doesn't mean "anything goes" though.
You can also argue proc ring being better for priests than mages because pretty much all of mages damage comes from ray of frost - meaning any proc outside of a ray of frost cast is essentially useless.
Also since "openworld" gear doesn't specify if it's openworld pve gear or openworld pvp gear, and since the offhand without stamina would be better for openworld pve, we can't really make a judgement call on the offhands.