Is diplomacy necessary?

I mean the same thing, okay, let's add one... or two neutral units from other castles, but creating a mixed army is pointless, IMHO, but if they offer diplomacy, literacy, or eagle eye as skills, I wouldn't hesitate to develop diplomacy, i.e., it's not in the last place for me...

Added 1 minute ago

I'm almost embarrassed to ask, but have you encountered level 9 monsters?!:)

No, I haven't, there weren't any)) and that's a pity... it would have been possible to create...