I'd be tempted to "brutalise" the AI tech tree for Tanks, and make it only build perhaps 2 or 3 models of each "selection" - eg Basic Medium tanks - the player has a choice of MG, 30+mm, 40+mm, 50+mm, short 75+mm (5 choices) or for Improved mediums, 40+mm, 50+mm, Medium 75+mm, Long 75+mm, 85+mm. For the AI, I'd probably restrict it to (say) Basic - 30+/50+/Short 75+ or for Improved - 50+/Medium 75+/85+.
Whislt I'm at it.. I would actually "prune" the gun tree somewhat - to me, there is no significant difference between a 37mm gun & a 40mm gun, especially for AA weaponry. I would classify tank/AT/AA gun as follows :-
Machine GUns :- Up to 15mm
Cannon :- 20-25mm
Light :- 37-40mm
Early Medium :- 45-50mm
57mm (6pdr)
Late Medium :- 75-77mm Short / Close support (HE only)
75-77mm Medium (AT/Tank/AA)
75-77mm Long (Panther, maybe 17pdr ?)
Heavy :- 85-95mm Medium (eg Tiger I/Flak 36, T34/85)
85-95mm Long (Tiger II, Pershing 90mm ?)
Extra Heavy :- 100-110mm (Mainly AA, but also tanks - eg Centurion)
Super Heavy :- 120-130mm (Jagdtiger, IS2, large AA)
Ultra Heavy :- 150-155mm (Maus, static AA)
Having studied the way things developed, it seems to me that much of the later development of the larger calibre tank/AT guns was driven by the pre-existing AA guns, which were a known entity, firing high velocity ammunition already in production, and then adapted to meet the ever voracious demands of tankers and AT Gunners for larger, more powerful guns.
Hopefully my categories cover pretty much every weapon people can think of ! (probably for most other artillery pieces too) I'm tempted to suggest that the 45-50mm and the 57mm are more or less mutually exclusive.. but I have a feeling the Soviets used 45mm tank guns and 57mm AA guns.. might be Ok, if they chose the different tech path for AA vs AT/Tank guns.
Any thoughts/ Comments welcomed.
Tim