Hmm, kinda hard to describe the dynamics of a 100p map to someone who never played it... but I guess I' ll try.A 100p map has 4 core cities. I' ve upgraded IC' s to 5 there, infra to 1, two have barracks (2 and 3) and two have airfield-2. 5 resource provs are in the process of upgrading to infra-3. No other IC' s built in core.
That means I control about 7 former major' s territories, and some minors. Landing in Africa now, but no significant ground there yet.
It seems to me that the dynamics of the smaller versus largest map is quite different. Different enough to make my commentaries about what @Hans A. Pils said about changing infantry invalid. Though for the maps I tend to play, the smaller and medium sized maps. The suggestion @Hans A. Pils makes would make absolutely no sense at all.
I wonder why you exclude commando' s from your " 5 infantry types" , they function like inf in many ways!
Commandos cost much less manpower, give a very big power output in return for manpower invested for far less upkeep than the 5 infantry types. They are well worth the manpower they cost while this is not the case with the 5 infantry types. Also, their being able to be built only in the capitol caps their strength quite enough. So commandos are just to much of a different breed to include among what counts as infantry (imho).
So you have 49 aircraft in interceptors and tacs combined and only 11 infantry. Their initial manpower cost look like this:
11 infantry: 14,300 manpower
49 aircraft: 19,600 manpower
The 11 infantry have 35.75 worth of planes in them in terms of manpower.
Now I am quite sure that it is quite simple to see that in terms of damage output, infantry is not a very good investment manpower wise.
Also, the 11 infantry have 165 HP when in full health. The 35 (rounded down) aircraft would have 700 HP. So in terms of HP, manpower is again not very well invested in infantry.
You could do the same when comparing them with SP arty. Having 11 infantry means you did not build 28.6 SP artillery. Again growing the same amount of manpower into more HP and power output. This time with a mechanic that lets you avoid damage all together.
Even if you add the food and oil consumption to this, the oil expenses are well worth the damage output and extra HP.
Infantry is just never a good investment for your manpower. So, making them cost more initial manpower when training them is not a good thing.