often there is a week of some creatures that appear on the map... and at least one army joins, and it's not necessary to have diplomacy... I, for example, never take it... because it affects the recruitment of creatures for money.
I think leadership is better... (if anything, it also affects friendliness)

Not necessarily-)
as far as I know, diplomacy still greatly affects the recruitment of creatures! In a random game, creatures don't want to join me at all without diplomacy, even native ones, even for money-)
But here, the Vision spell is important - it's a very useful thing - it shows everything you need-))
leadership does not affect friendliness!! - this has already been said many times somewhere-))))
leadership is increased by simple artifacts and some structures on the map, and also decreased by other artifacts (far from being relics), so it is not a fact that the leadership skill is necessary for a hero0)))))

Added 1 minute ago

to Joshua:
If we're going to delve into this, let's define what tactics we're going to talk about, because they are different, for example:
1) the tactic of playing "for fun" against the AI
2) the tactic of playing "for speed" against the AI (regular offline Tournaments)
3) the tactic of playing against a human
etc.

-))) that's reasonable!
I suggest discussing the tactic against a human, but with several AI players on the map - this is the most common situation for me..
tell me, is playing against a human not "for fun"?-))))))))

well, if you think about it, the developers approached it very harmoniously, not giving the Tower a hero like Alamar or Jeddite, otherwise it would probably have been the strongest city from the beginning-)))