Players will change the way they interact with heroes as it's kind of clunky right now.
Lower level heroes with have a quest type of mechanic to get levelled up. As the level increases so does the boost provided by the hero.
We tried to confirm if increasing the level also increases the rarity because that would be a disaster for event buildings already acquired. As of Tuesday Feb 3, 2025 the response was, "a qualified no" which means it's still up in the air but as of then no. So we'll see.