Yeah, looking at all that math...I think hundreds might be a bit low if you really wanted OOBs even just for all the at least semi-reasonable combinations...
Each of rifle, MG, and RPG with or without some support of the other two is 12 basic foot infantry compositions.
Each of those 12 could have organic support from one or two of pretty much any of the other units in the game but even if we limit ourselves reasonably the list might be:
AT gun, artillery, assault gun, heavy tank, monitor tank, tank destroyer, buggy = 7
so (12 * 1 for no organic support) + (12 * 7 for one type of support) + (12 * 7 * 6 for two types of support) = 12 + 84 + 504 = 600 OOBs for foot infantry.
Each of rifle, MG, and RPG in trucks or APCs -or- motorbike infantry with or without some support of one or two of of the others (limited to trucks or APCs) is...79 basic mobile infantry compositions I think.
Each of those 79 really could have organic support from one or two of pretty much any of the other units in the game...let's see if we just add a few to the list above:
7 + light tank, medium tank, SPG = 10
so (79 * 1 for no organic support) + (79 * 10 for one type of support) + (79 * 10 * 9 for two types of support) = 79 + 790 + 7110 = 7,979 OOBs for mobile infantry.
I could go on to armored formations but yeah...
(I mean I haven't even been including jetpacks, robots, walkers, and rockets.)
Doing this math has actually convinced me that the only real path forwards must lie in some combination of customizability and procgen.