I think that for a more fluid game we need cavalry units as well as adjusting the price of tanks. Tanks are devastating in large groups, but it’s hard for most nations to produce large groups of tanks at 6 ipc’s. Plus the early game is pretty monotonous with only masses of infantry and artillery attacking and counter-attacking. Cavalry could help spice it up a bit, maybe with 1/3 atk/def and a movement of 2 with blitz. If they cost 4 but could be boosted by artillery, they’d be a fairly viable unit but would probably fade a lot when tanks arrive.
To say that cavalry played a major role in the war or even that it had an equal level of survivability as infantry is a misstep at best, and revisionist at worst. Cavalry units were consistently BUTCHERED against machine gun-defended infantry lines, and quickly became obsolete. I actually think that the omission of cavalry from this game is one of the better choices of the designer. The early game is “monotonous” (as you’ve put it) with infantry and artillery, because the early WAR was “monotonous”; 1914-1916 was a period hallmarked by mass artillery-supported infantry attacks.
Now, I will grant that on the Eastern Front (as well as in other parts of the world, Mid-East, etc.) cavalry played a slightly greater part than on the Western Front, but I still don’t think it is worth adding an entire other unit to the game to represent this limited role.
If you ARE going to represent cavalry in the game (which I don’t recommend), you must then differentiate between entrenched infantry and mobile infantry, and make the cavalry 0 attack against entrenched. This is the only way it would make sense.