Hello, And G.
I've been playing Age of Wonders for roughly 7 years now -- multiplayer for that matter, never really touched the campaign. I also play IniochReborn's mod (highly suggest looking at it) so the meta is a little different, and the ruleset would definitely need a complete rework for your changes; and that's fine.
The primary problem with your ideas are that people don't want a campaign rework, they want a multiplayer rework (myself included). That's why you're seeing so many ideas that heavily conflict your own. That's also fine, though. Because if your dream is to reshape the campaign, then by all means!
However, my circle play on Emperor, and auto-combat only. It was the only way to balance things out for the A.I., and we also only play the scenario After The Fall. One of them tends to die a lot in crypts, while the other two of us tend to die a lot in 1/10 odds of winning a battle to level up our leader. We thoroughly enjoy the, "high risk, high reward", combat. Although, I still miss watching the A.I. spam cast Terror, it was scary..!
Significant notes, in regards to the ruleset (in my opinion) include: Human Air Galley being turned into a fast transport unit, because it was insanely OP, and everyone would always migrate over to Humans for that reason alone lol It sounds bad now, but it's great for ambushing people, especially their super leader. Boats can only shoot arrows, for the same reason as the above, due to Free Movement. I suggested that the Lizard Men have a Battering Ram turtle, because it made no sense why they didn't already have one. I also suggested that a few level 4 units have ranged attacks that made sense to their lore, to help fight dragons, because their also OP.
People like having a Demi-God leader, because it's fun. We like starting off with, and obtaining a decent amount of skill points, because it's a roleplaying game, that should have build diversity. You want to start off as an HP Tank with Regeneration, and terrible Attack? Ok. That's my main build, anyways. I mean.. are we really talking about realism in a fantasy game lol You can't buy health, use magic on machines, you move painfully slow, and your level ups are unrewarding? Gah. There are better ways to address this, instead of nerfing leaders to hell.
Instead of making this game only about spamming archers, and shunning leaders - I'd say:
1. Either cap HP at 15, so that your leader is actually capable of fighting alongside his breathen, and not being nearly immortal with 30 HP - or give items such as Chest Armor, and Rings upwards of a +3 bonus, so that you can have 16 HP (bonus depends on rarity, so you at least have 12 HP, if you're lucky).
2. Another thing - why limit the capabilities of magic? It's magic, it defies realism lol .. That's the point. If we're talking about realism, though - then leaders should inherently start with Leadership.. because their supposed to be the one's leading the armies.
3. Increasing the cost of Moves from 2 to 5 seems too extreme, as you'd essentially be waiting two level ups to move a single hex faster.. not to mention trying to traverse caves. I'd suggest keeping it at 2, and capping it to 42 moves. That's another moot point to realism in a fantasy game, because a horse shouldn't be able to move nearly twice as fast as a dragon lol
4. Level ups are a tricky one. I haven't played Age of Wonders in months now, and don't currently have access to my laptop, but I'm hearing that you receive 40 skill points at level 1? I'd suggest 1-5 requiring 5 experience, 5-10 requiring 10 experience, 10-15 requiring 15 experience, 15-20 requiring 16 experience, 20-30 requiring 18 experience. At level 1 you have 45 skill points to spend, so that you can choose an useful ability, and still have some room to build your character. The leveling system is a little more modern now. You level up fast in the beginning, and have some trouble maxing out, but it isn't impossible. Levels 1-10 give you 5 skill points, and 10-30 give you 10 skill points. So, you're leveling up fast, and you're strong, but you aren't becoming a Demi-God any time soon; but.. it's still very possible, which keeps the gameplay interesting.
Lastly, I'd like to touch on defense. Doubling the cost from 5 to 10 also seems too extreme. It's really useful to have, but it shouldn't take you the entire game to acquire. Especially as maxing out defense will be a lot riskier now, due to the HP being only 10, and whatever hits you will be a critical hit; so, it'll probably nearly kill you, if not kill you. I'd suggest the cost of defense being 6, instead of 10. That way, you at least have 3 defense in 3 level ups, instead of 3 defense in 6 levels ups. Both are an equally long time to help protect your fragile leader.
This way, it gives people less incentive to immediately cling to Earth magic. Stone Skin would be game breaking, despite it already being insanely useful, and let's not forget about Entangle.. shouldn't need to elaborate too much there. Earth magic is already arguably the best with those two spells alone. At this rate, the only way that I see people using the other Spheres is by preventing them from cancelling each other out -- but I'm not even sure if that's possible, along with half of what I've suggested..
I don't really have anything to add to the walls, terrain, cities, morale, etc. They all seem interesting so far, and are still being thought out.
Best regards to you, And G. Humbly - Alcedes1611