I think that it's more about the fact that some units are more or less useless in HOI3 despite having distinct and important roles IRL, e.g. ATs and AAs. You can run around with ARTs only and do more than fine and you "save LP points" by not researching ATs. This suxx. Of course you can pretend that it's not the case, but why should you? Other units that were effective IRL are only useful in gamey, unrealistic combinations, e.g. all-HARMs units because of their low softness. This is a typical example of bad balance and it is not historically accurate, either.I can't see why you are complaining about units then, because to be frank all the units in HoI3 do have their place for being useful. Any player worth his salt will know when to build the more specialised units. Of course the weapons of WWII were 'unbalanced' and that reflects in the concept that some of the units are in general, far superior in the general sense compared to others. All that your argument appears to be based on is; 'A gamey player will only build X, Y and Z, when there is also A,B,C in the game; y u no luv A,B,C Paradox?'.
I make a joking comment there, but the jist of it is like the punch line; if units A,B,C were not historically 'that useful' then they shouldn’t be 'that useful' in HoI either. Since units like AT, Engineers, Battlecruisers, Cav, Militia etc. do have their place for certain nations and strategies. Then they are; "...useful at least in some circumstances." which is what you claim you want... ¬.¬
Another problem is that uber-specialisation is everpresent and everybody is building 2 ship types unless they are RP or playing a heavily modded game (but even then uber-specialisation may still be common). It's similar in case of air units.
IRL every major army/navy/airforce in the world was and is a mixed force. In HOI3 it's the opposite.
Lastly, if the game makes no effort to fight hindsight, then it will never be properly balanced or realistic. Building only CVs from the start is neither historically accurate nor balanced. We will always get flawed results if things are kept that way. It's even worse when the AI is told to always make the historical decisions, even if they were not the best ones.
There should be mechanics in place in order to encourage/force the player to build BBs, just as not everybody should be using armoured divisions in Blitzkrieg action. Otherwise, I think that we are all just pretending that there is sth called "choice" and we can just as well remove half of the units from the game. It gets boring when I start reading another AAR and see that everyone believes that CVs are the future and that the next war (which will come in 1939, of course - everybody knows that!) will be decided by rapid armoured breakthroughs and massive encirclements.
You cannot seriously expect that a player will deliberately constrain themselves by building inferior unit types, because, well... why should they? IMO the game should put the player in a position of a given country and they should face similar constraints as RL leaders did. If there were good reasons to do X, but with hindsight we know that Y was the better option, then X should be a very tempting choice in-game.