I have played every Amplitude game, and most other major turn based 4x games.  Human kind is a good game. It's worthy of being a great one, and thus worthy of critiques.

I propose adding two filter overlays to HK.  "Prosperity" and "Logistics".

Prosperity is a hex by hex map of land value / quality of life / speed of the local economy / trade .    

Logistics is a hex by hex map of the supplies and foods and munitions needed to move armies and fights wars.

Prosperity is largely automatic with reduced user control/manipulation, and Logistics is more user directed.

Luxury resources / World Wonders / Religious cites / and most districts produce some small amount of Prosperity per turn.

Towns produce food, that can be converted into war supplies (sources on the Logistics filter), or consumed for growth (at a rate proportional to the local population) or converted into additional prosperity production.

Prosperity flows every turn out from sources from hex to hex. The rate at which it does so depends on the local tiles.  Cliff faces block Prosperity flow, differences in elevation affect the preferred direction. Forests slow the flow in and out of a hex, and rivers and roads accelerate the flow 'down' them more than up them and pull in prosperity from the hexes across them. A river would have higher prosperity at the mouth of the river to a local lake then at the source and hexes 2 tiles away form a river would be more likely to send the prosperity towards the river than away from it each turn. Farms tend to exclude prosperity pushing prosperity away from themselves.

Towns and merchant districts pull prosperity from many tiles around them, and consume some to produce money.

Towns that have high prosperity unlock and build for free infrastructure. Hexes that have high prosperity develop roads of increasing effectiveness as the prosperity rises.  

As a result prosperity will tend to follow rivers in the early game and follow connections between towns and luxury resources and monuments or other sources of prosperity.  Building a new merchant district encourages the development of roads locally, but reduces the overall prosperity locally as it gets converted into money (tax).

The player can expend resources to directly build infrastructure (including roads) with money and town production, but no longer needs to build EVERY building and roads by and large happen gradually and organically rather than spontaneously.  

Diseases spawn in areas where there is lots of food production but low prosperity and spread along trade routes.  Diseases start benign and get worse, so that towns local to the outbreak get exposed earlier but develop more immunity to the weaker strain to reduce the impact of diseases being too RNG for most 4x games. players can manually shut down trade to limit spread, but that limits prosperity production and flow to markets thus reducing money generation.

Contrast with the Logistics overlay:

Strategic resources, Makers quarters, some wonders, and mostly towns produce war supplies.  War supplies travel using the same type of logic as prosperity, but with different modifiers. Supplies are pulled in strongly by depots, military infrastructure, and roads and travels very poorly between undeveloped tiles and tiles without roads. The user can build or establish and plan war supply lines dotted with depots and defensible locations (potentially even fake depots to trick other players about where attacks might come from).

War supplies are lost every hex they travel, less along roads more across undeveloped tiles; and are consumed by troops (less by stationary friendly troops more by troops that need to be re-activated to move again in a turn or healed from combat, and most by unfriendly troops).    Troops in hexes with high supply levels take less damage from incoming attacks (don't deal bonus damage back only reduced incoming damage).  Advanced troops can get larger overall defense bonuses from supply than primitive troops which need very little and can use very little.  Troops in hexes with low or no supply levels are easily destroyed or captured as POW's.

Overall:

-----This enables deeper strategy as players balance high level war supply production against growth and prosperity generation.

-----Reduces the number of user clicks to develop towns as prosperity directly converts into free infrastructure as it hits milestones.

-----Makes market squares less arbitrary and gives more hexes a meaningful money production ability.

-----Rationalizes and makes organic road building and trade

-----Enables realistic feeling disease mechanics that don't completely disable the unlucky RNG looser of the plague lottery

-----It enables much much deeper Tactical game play as each hex in the battle map has unique and turn by turn changing levels of    supply provided defense and allows for encircling maneuvers gorilla tactics like strikes of primitive units against late tier units

 that failed to properly defend their supply lines roads and depots.

-----Makes shared planned supply routes between allies meaningful and measurable so that after a war it can be directly measured how much each player contributed to the war effort as measured in troops supplied and supplies provided.

-----Allows late game wars to draw in troops from across the map very rapidly to allow for truly epic scale wars where you are not

waiting 10-12 turns for your troops to finally arrive at the war front only to discover your opponent has developed and built a

new class of fighters and you're doomed.

-----Provides a natural way to resolve 'how much territory was won' as a result of wars based on which player is providing the most local supply to that district, rather that a  war-score per district claimed that depends on the type of district have it discounted by the amount the winner 'controls' the land as measured in supply power in the land.  

-----Naturally connects troop maintenance to food production back home without conversion to and from money.

-----Naturally  addresses the late game food surplus

-----Verisimilitude and core mechanic uniqueness that would make HK feel and behave incomparably to other 4X offerings that a Magnum Opus truly deserves.