I never considered the prayers to be overpowered, especially when looking at what other armies have. Heck, most of the time they get dispelled in 8th edition anyway. It always felt annoying (and time consuming) to me that you need to cast every turn. So in that regard also a Remains In Play would be nice. But to not make it too overpowered, cancel it when you choose to do a new prayer.
And in general, yeah, I love Empire Warrior Priests. I have all the metal models, which were very nice, in my book.
What is the 'Blessing of sigmar' mini-diorama?