Let's all calm down and discuss things with arguments.
I believe we can all accept valid arguments and I do understand concerns about the potential "unhistorical" mix of civs in the game. In fact playing kushites or ptolemies in arctic biome maps does not really make much historical sense (poor elephants! Oh - and even trying to grow crops and rice in the arctic is rarely providing much yield). So plenty of examples for unhistorical, unrealistic combinations. If looking for more realism, it is indeed possible to select which map is played with a selected biome and also which civs exist in a game (at least for SP ).
A very valid counterargument is certainly, that certain entities/roles/unit rosters, building types and technologies did not exist in all civs and as a consequence it is more difficult to establish the right balance (as an example, personally, I am not really sure that gauls or britons had a navy able to even nearly match roman or greek warships).
So, indeed balancing civs of such different levels can be a challenge for establishing good gameplay. A clear counter tech needs to be identified and implemented for such cases if one can be identified.
What I personally also do like, however, is the approach to re-use the game mechanics and framework for another focus on another region or try combinations for the fun of it. Anyhow, it is fascinating reading about different more or less well-known ancient civs that are being discussed in this forum. I feel really motivated in learning more about those, so I clearly welcome such opportunities. And if someone even intends devoting some time in developing this civ into a mod, very welcome! I would be interested in seeing and playing these.
As already discussed in this forum, at some stage it may be desirable to split the game into different scenarios or phases (a bit like AOE?). I believe XIIIAD mod already made a move into that direction, as well as the Aristeia mod if I remember correctly.