I red all this page https://en.wikipedia.org/wiki/List_of_map_projections to find the best projection.  Some considerations that bring me to chose sinusoidal:  Sinusoidal is an equal-area as well as Lambert projection. Lambert is perfect till the first 45°, then is awful: to preserve areas it changes some states too much, like Australia. I start from Tangarm heighmapper. I searched a lot for alternatives with other projection, but there aren't. Tangram uses Mercator without geo-reference or GeoTiff, so I have only a png, and I changed it to a pseudo-sinusoidal manually. In the future I can use a real sinusoidal through a python script to automize the reprojection and apply what I learned in these two years (color curves in GIMP, ...), but for  now I'll not recreate it. It's a too long work. 

I’ve never played AoE, so I wouldn’t know…

They are much more unique now than they used to be, the exception being maybe in A23 and before. Some civilization have more unit variety, others have stronger upgrades for fewer units. Analogies being Kushites for the variety and Spartans for stronger, but fewer unit types.  Balance is a hard thing to master, so this game tries to offload uniqueness onto civ-specific upgrades and bonuses. If you think civilizations are mostly the same in 0 A.D., then you must believe that civilizations in AoE2 are almost identical.

For sure, I’ll make a short mod and post it here showing off some of my balancing ideas as soon as I have time.

You are certainly right - there could be more civ character diversity. However, balancing appears to be a MAJOR task and I remember loooong and excited discussions and changes back and forth to arrive at the current more or less stable state. Possibly, with your modding experience, do you think you could generate a few  of your proposed test changes and let players look at the resulting balances?