I recently learnt about this game and really love it. I really love the style that battle actually happens in a "minigame". After watch opendev videos from different plauers,  I humbly raise some questions about the current battle system.

1. In the current system, battle happens as a "minigame", in the same map as the compaign map (the map you see where you are not in battle; I do not know how to name it). Each turn consists of five rounds for the battle. The fact that units can move much more (*5) distances per turn in battle map than in compaign map, plus the fact that the compaign and battle uses the same map, making the battle system seems unrealistic sometimes. In one video I see both aztec and khmer armies bordered Oxenford. Khmer sieged the city, and then in the battle map, the aztec army just disappeared though they still occupy a certain tile in compaign map. I pretty much like the battle "minigame" as it adds more possibility to win your enemy even if your army is outnumbered. My suggestion is, if time allows, let the compaign map and battle map be of different scales/resolutions. Specifically, when you enter a battle, you jumps into a "zoomed in" version of the map that covering tiles within of a few radius of the place where your armies stand by, which somehow similar to total war series, but humankind is a turn-based battle while total war is a real-time battle. 

2. The reinforcement seems bugged sometimes. In some videos, players can put a unit at the spawn point of enemy reinforcement and enemy reinforcement will not arrive. In other videos players surround the spawn point of enemy reinforcement such that every reinforcement is immediately destroyed upon spawning. I guess it's not a realistic idea to set the spawn point in the middle of map, which brings two consequences: 1. reinforcement spawn point can be occupied by enemy; or the spawn point can be surrounded while still spawning reinforcement, as if the spawn point is a magic portal; 2. Provided the spawn point is not at good terrain, one can wait at the spawn point to easily kill off the reinforcement, while poor AI still keeps popping up their reinforcement. My suggestion is: always keep the spawn point of reinforcement out of reach for the enemy (for example, in the border of the battle map) such that one can have enough space to  easily pulls out his reinforcement in the first round of battle.

3. Retreat. As discussed in other posts, one shall given the possibility to strategically retreat from battle; For examples, I have a group of fast moving horseman and got caught by a group of slow moving but powerful anticalvaries. I perhaps just want to circulating these anticalvaries in battles or just flee from the battles. Retreat may save your units, but should come as penalties, for example loss of golds (looted by your enemies); or as suggested by other posts, retreat can only happen at the next game turn so that you must stand your enemies attack for one turn. You may also think you can not retreat from sieging battles; otherwise you will lose your cities. You may also not retreat if all retreat routes are under enemy zone of control, etc... There are many possibilities. 

Overall, I'd like to say I love the battle system already and I preordered this game on steam. Due to limited time to release, perhaps it's risky to do any large changes on the battle system. What I'm writing here is as an old strategy game player, some personal ideas for possible improvements. I wish humankind goes well and release at the scheduled. time.