Also that startEntities.length - 1 causes every civ to have 1 cavalry but britons 2 cavalry + 1 dog and mauryans 2 cavalry + 1 elephant. So adding a check for infantry + females.

"What do we do if we need twice the number of starting units?"
Change the starting entities of the civs if you want it to be for every random map.
If the changes should be for one map you can either change the startEntities argument instead of just using getStartingEntities().

It is unclear to me what you are trying to achieve here though since this is a map file. If you think the starting entities should be changed for this map propose a patch.
Similar for the starting entity placement functions in the libs (if e.g. placing more than 4 unit types causes problems or something similar) if you'd suggest to change the starting entities for multiple maps (though no entities should be hardcoded there IMO).
If you want the staring entities changed for all maps change the civ files entry accordingly. Make sure that the placement functions in the libs work with the changed entries in that case.

I haven't seen Spahbod, the creator of this map, for quite some time so I'm not sure this concern will be picked up by the author.

placeCivDefaultEntities() might not have existed at the time of commit which would explain the "copied" part (changing that and createStartingPlayerEntities() to use optional arguments could be worth a commit IMO).