I don't think more
historical units had broken gameplay. Even it adds more flavour and smile (at least on my face
) when i can use historical and flavour units - if it won't i would just stay with civ's standard M4 Sherman, Supermarine Spitfire and Avro Lancaster - less work but imo also less fun.
It didn't broke gameplay, also because AI still chooses stronger units to build. The same option is for Human Player.
And units have different parameters (different parameters were used for different units combats: tanks. bombers, fighters, artillery) - depending on speed, armament (type and diameter of gun, number of MG - more provides additional strenght agains human units), thickness of armor, weight, number of built units, size of the shell, rate of fire, range, weight of carried bombs. I've put much time to this system to make it +- historicly correct, and sorry, but I won't change it to RTW clone where everything is more simpliefied. If it'll apear it will apear as standalone mod's mod, surelly i won't put so much effort into those units' xml.
For MachineGun - I was thinking about it too - it's weird to shot air units with land MG (tough possible - it's not the problem to penetrate even metal surface - so the pilot can be killed
). IIRC ability to shot down air unit with MG was introduced in patch 3.13. I left it right now, but it seems the ability to intecepting air units should be decreased (maybe to 10%).
What do you think? Leave this option weaker or throw it away?
For ships - yeah it could be more diversified. But I don't plan to change it soon.
I didn't have idea this option exist when realising mod. Will be fixed that way in next patch, until the events in Python would be added - managing much better with peace and war declarations.