When there are strong neutral creatures, it's probably not beneficial to accumulate troops; under such conditions, other strategies like artillery, magic, or hero attacks (in offense), and even ranged attacks, will perform much better.
1) It's unclear which city to tie it to: there are many.
- To the most developed one in order.
- To the one that came under the player's control first.
- Provide a selection menu with a script.
2) The hero gives a bonus to the city, but not to their own army.
3) There's a significant delay: you get the skill on Monday, but you only get the benefit a week later (if the game hasn't ended by then); this significantly devalues it.
The current solution is simpler, more elegant, and more interesting.