Personally I would quite like the whole tech system to be completely upended and changed to be more true to life. WW2 tech was really all about stuff that barely registers in the game. Most basic weapons used in WW2 realistically had 2 generations at most. Everyone started the war with a rifle and we the only real change was Germany starting to mass produce the SG44. MG development was basically production engineering. Artillery was everyone replacing their WW1 gun models. The real tech stuff was split into to lines of activity are development of additional infantry weapons (RPG stuff), new munition designs, steadily improving aero engines, radar stuff, improved radios, radar, air navigation and so on. I feel like the game would gain a lot in terms of WW2 feel if the basic weapon systems were basically just there and tech was all about adding icing to the cake.
For example, tank design wasn't the result of developing underlying technology. It was more like specifying a tank design (ie design it in the in game tank designer) and then what 200 days for the design teams to actually turn out a design which ends up being not quite what you ask for. Spend some more design time effort on improving it or throw it away and start again. The actual tanks you see each side using where the result of reacting remarkably slowly because of design time to the equipment encountered in battle. In HOI4 I just develop the base tech and then when I see those T34s I can instantly react with a design of my own and all the delays are the time it takes the factories to adjust.
To some extent there should be similar pattern in aircraft design except the air war is so much about engine design. The Germans had lots of aircraft types (eg all the MeX09 designs) that simply weren't better than putting the better engines into the old designs.
Infantry armament, there was at least 4 "main" types. Bolt action, like in WW2, semi-auto like Garant, Soviet SVT38 and SVT40, German G41 and G43. Submachine guns became relatively widespread for specialist troops and backline troops. STG44 was a forth type, intermediate calibre assault rifle.
Semi auto rifle proved too hard/expensive to equip all troops for most countries, that were not USA, Soviets and Germans being decent runner ups.
Tank design was largely beholden to engine power, dimensions and suspension.
It wasn't slow reaction, it was a case of new engine with significant power boost requiring years of development and testing.
Despite Char 2C and King Tiger being same weight class, the later carried far more useful load(gun and armor) then former, being just 19 or so years apart.
Same thing with T-34/Pz4/Sherman vs Char B1. Same weight class, but later designs far more capable.
And, despite common stereotype, BF-109 went through huge redesigns and by mid-war was barely hanging in in a fight vs allied fighters. Because new planes had better engine power for same dimensions, and lower drag. Same year Mustang could outfight BF-109K4 quite convincingly, despite having twice the range and heavier armament.
.png){kind=avatar}
