The mongol UT (Nomads) are not very useful. In AoE4 they are very nomadic with full pop like the Huns and an unique drop site, the Ger, who can research economic upgrades.
In Aoe2 there is numerous Yurt model. It’s sad than the Mongols can not build Yurt, so I propose for the Mongols :
Remove Blast furnace (garrisoning sheep in the Ger give attack to cavalry melee unit like the relic bonus of the Lithuanian)
Remove House
Give them Ger (a model of Yurt) Ger have less HP but cost cheaper. Also they cost a little food (because yurt are made from part of wood and part of wool or leather. They are building faster and can serve to research many technology and unit upgrade
Ger
Cost : 15 wood and 5 food
Take less time to build (20 s)
HP by age : 450 / 550 / 650 / 750
Armor by age melee/ranged : -2/6, -1/7, 0/8, 2/9
Can garrison 5 sheep but don’t produce food like the Gurjara mill
Instead of producing food they increase the attack of melee cavalry unit by +1 by sheep (limited to +4)
Can research technologies related to cavalry : Bloodline and Husbandry
Can research the technology Loom (related to the sheep)
Mongol player can deposit food in the Ger
Can serve as one of the required buildings to advance to the Feudal Age
For the UT Nomads
Remove the cost of food of the Ger
Destroyed ger still count as pop cap
Garrisoning sheep produce food
Ger can serve a drop site for all the resources
Can serve to research the technologies of mining and lumber camp
Can serve to research the technologies : Handcart, Wheelbarrow
Can serve to research technology related to archery : Ballistic, Thumb ring Parthian tactics
Can serve to research unit upgrade related to mounted unit : Heavy cavalry archer, Light cavalry, Hussar, Heavy camel rider, Elite steppe lancer, Elite mangudai (I don’t put Cavalier because mongols focused more on light cavalry)
At final Ger is a replacement for the House who cost less, have less armor and Hp but give you attack bonus for your melee cavalry. It’s cost food but the food cost is compensate by the UT Nomads. Also the building can serve as drop site first for food and then for all resources. Ger also allow you to research upgrades who save time in your military building and Town center to produce more military units or to produce more villagers.
With this version the only worse thing is than their infantry units deal less damage.
Version without removing blast furnace
It’s the same version than above except :
Don’t add attack bonus from garrisoning sheep
Don’t remove Blast furnace
Allow Ger to train sheep (100 food)
Nomads UT allow Ger to train cow (150 food)