I think AoMR should have the ability to gift military units to your allies.
Technology issues
The main issue is currently that not all civilisations have the same upgrades, especially Egyptians.
I think the solution for the Egyptians is pretty simple:
- Medium/Heavy/Champion Infantry/Archer/Cavalry upgrades apply to Egyptian Infantry/Archers/Cavalry
- Researching Spearman+Axemen upgrades activates Infantry Upgrades
- Researching Slinger+Chartior upgrades activates Archer Upgrades (Medium only needs Slinger)
- Researching Camel+Elephant upgrades activates Cavalry Upgrades (Medium is free like for Atlanteans)
For the Norse researching both Infantry and Cavalry Upgrades unlocks Archer upgrades.
This way you can get all the important upgrades for units of different pantheons.
This would also be helpful in campaign missions where you get some units of other pantheons or for Atlanteans using the Traitor god power.
Also maybe a future civilisation will have the ability to convert human units like the Chinese Monks in AoMEE.
How gifting could work
To prevent the feature being abused in the early game it could require a Market being build or maybe even the Ambassadors technology being researched.
It would also not be possible the gift Economic units to get around the villager train limits.
Other units with a train limit like Greek Heroes, Pharaohs, Oracles and Dryads would be excluded from the system too.
I don’t think Norse Infantry really causes an issue. It’s convenient to have units be able to build and repair buildings but they can only build the buildings that both civs have in common.
Also Norse Heroes do passively generate favour but that’s ok since the person gifting them loses the favour generation.
Gifted Priest can not empower buildings because that feature is exclusive to Ra so that is not an issue either nor is their haling ability since they can heal allied units anyway.
Not sure if I forget any potentially OP units. Some units would benefit from some Minor God technologies that are applied to a whole unit category like all Heroes or all Infantry but I don’t think they would be OP either especially because they only appear in late game.
Would be gifting all your human units to a Norse player be OP so they can get more favour? I don’t think so.