It is also worth keeping in mind that even Germany, who had a bit of an armor fetish, only deployed 19 panzer divisions for Barbarossa, compared to more than 100 infantry divisions. The 40W tank meta of pre-NSB resulted in a much higher proportion of armor for most nations, with infantry divisions being left much weaker (little to no artillery/AA/AT) and less numerous than they were historically.
The absolutely biggest problem in HOI4 is complete lack of any combined arms bonus. The idea of building each and every independent units to be a mix of various forces was one of the biggest changes in doctrine between ww1 and ww2.
In reality, by mixing infantry, artillery and armour in single unit you are not adding combat value but multiplying it. Infantry without tanks is easy prey for artillery and machine guns, tanks without infantry can be easily defeated by entrenched infantry with artillery. And Infantry and tanks without artillery would have major problem to even engage as they would be constantly disrupted by enemy artillery.
If there was any combined arms bonus in HOI4 (like there was in HOI3 for example) we would see much more realistic division composition. Organisation in theory is doing it, but with tank org boosts from doctrine make it inconsequential especially as tank divs do not need that much org as players do not use them for defence.
Another missing thing is command and control. In reality, oversized divisions should suffer reductions in combat power. That's why in reality division size was standarized around 9 inf battalions with around 50 barrels of artillery, or in case of tanks 150-300 tanks with 4-6 infantry battalions. Massive 800 tank divisions (40W tank) as used by many players should be getting devastating penalties from C&C to the point where they are objectively worse than realistic 4xArm 6xMot 1xArt/SPArt.
Unfortunately, both of those problems are result of design decision that player should be not penalized for creative use of division designer. That's why basic stats are simply additive and this, by simple mathematics, give bonuses to bigger divisions. This clearly was not planned effect, so for NSB they tried to fight this with complicated CW and combat calculations.
Tank designer is victim to similar problems - first Pdox gave players option to produce completely unrealistic stuff - for example heavy tanks with massive guns and light tank one man turret or vehicles with massively OP SA and then try to rein it in by ludicrous cost of tanks. Why, I may ask, there is no code to make some module combos impossible? Why it is not possible force big turret for big guns? Why the cost of chassis is not tied to the amount of stuff you place on tank? The list go on.
This cost inflation would not be necessary if in the first place division designer wasn't promoting vastly ahistorical, corps-sized "divisions"