Which is stronger, a Castle or a Conflux?

However, as I understand it, you, Sir Forrest, rely exclusively on online games, right? Then it's hard for me to imagine that a hero in your battles manages to gain a high level. For battles on the map, secondary skills, such as "magic...", are not as necessary as in a battle with another player; therefore, there is still quite a decent amount of time to acquire the necessary skill.
and, most importantly - (this is purely out of my own interest :)) Do you often conduct the final battle with your main hero?

1)
It's not quite clear where such conclusions about the hero's level come from.
The hero's levels are usually as follows in online games:
1-1-7 (6-9)
1-2-7 (12-20)
1-3-7 (18-21)

2) The final battle is a subjective concept. (large is not always final) but I personally always use my main hero. If you are caught with a large army and not with your main hero, you will be considered the main hero.

P.S. In online games, merging is highly valued because it allows you to learn what you need in the middle and at the end of the game (and especially at the start)