yes, diplomacy often comes naturally to people, and if they have it from the beginning, it's even better... and it's more reliable than Inferno can boast!!
Bless is a simple, but good spell on expert difficulty...
it doesn't always appear in the Guild of Mages for Inferno... it's definitely better than Bloodlust, because it affects both archers and melee fighters...
you won't believe it, but at the beginning of the game, I like Bless more than Inferno; it consumes much less mana and can be applied several times, so the total damage inflicted by blessed units can be significantly higher than a single strike from Inferno - I repeat, this is at least for the beginning of the game... when there isn't much mana yet.