The combined arms mechanic -- as introduced in TFH -- was such an important feature. It encouraged the player to build diverse historically accurate divisions. I cannot imagine they would not carry that feature forward to HoiIV, especially with the more detailed division builder. Then again I would never imagine they would strip fuel from the game either. The fact that you can defeat the Soviets with all infantry no artillery divisions "because they have more org" is not particularly encouraging.
The piercing mechanism was good, though there wasn't really enough feedback to the player to let them know how important this was - unless you read the forums you probably wouldn't have realised it.
There are other, more intuitive ways of implementing this though. One is simply to designate some terrain-types as "close" and use a separate close-in attack/defend stat for combat in those terrain tpes (this is the solution used in Panzer Corps). Since the infantry excel at close-in fighting and have low stats otherwise, you are encouraged to use infantry to defend in the "close" terrain and to avoid using tanks to attack infantry in close terrain but instead attempt to out-flank dug-in infantry.
For example, using tanks to defend a stretch of desert is OK, but defending a city should instead be trusted to an infantry division because a city is close-in terrain. Attacking infantry in the desert is a task best given to a tank division, but assaulting a city instead favours infantry, with tanks employed to out-flank through open terrain.
In HOI3 it was possible to simply blitz the world with pure leg-infantry and not even build tanks. Or aircraft for that matter. You weren't punished for not even employing armour.
