First look at https://gitea.wildfiregames.com/0ad/0ad/src/branch/main/binaries/data/mods/public/simulation/components/UnitAI.js I think the first thing you will need is some tools that allow you to quickly search for a certain keyword in ALL files in 0AD.  For example, inside UnitAI.js you would see cmpAttack.IsTargetInRange, then you need to search for where is it defined.  You will be keep moving between many files, and up and down within a 5000 lines file.  You will easily get lost if you don't have a convenient tool. I personally use Emacs, but I don't think you will want that.  Perhaps ask ChatGPT if they have better tools suggestion for you.

This is how civilizations begin in 0AD. First approach is a factionless civilization, something generic...

Thx for the clarification. I was already suspecting something like this. It's a bit sad for me that they are not part of the Germanic civilization since they are probably the most famous tribe for the average player.

There should be some design in campaign mode that says "under construction".    

they ALSO have a massive damage multiplier on top of all that. also,all ranged cav has one extra pierce resistance than their infantry counterparts. combine this with the extra hp and mobility and you have the best unit for survivability