I feel like it should have some balance though such as the shrine needing to be max level before you could bless the thrall and it costing quite a few resources but i do agree that being able to bless your thralls would be a pretty neat feature and it should be fairly beneficial to entice players to use the feature though i will admit it being a permanent blessing might not be the best idea because that would change pvp way to much as everyone would start blessing their thralls and the people without blessings would be cut down i feel that if it were temporary then it could be used right before you raid a base or about to fight a boss and maybe it could work similarly to the demons where when they kill something using the blessing it would add to the timer. Just some ideas to add on but overall i do like your suggestion its an intresting idea that could work if implemented correctly in the game.