There are no engineer units? As a former Ranger/paratrooper, it pains me to say this, but 12B's are pretty damned important!
Engineering operations can be complex, and as long as the game relies on the 'dynamic' AI opponent I don't see engineering vehicles being added to the game, because many players have very high expectations when it comes to the AI opponent performance.
However, I believe it's possible to add individual engineer units by enabling the 'engineer' attribute in the database. That way you can have infantry units that can breach obstacles. The official data set doesn't use this.
Some tanks can have mine plows for clearing obstacles.
No NBC? Try running around for a couple of days in a Jenny Craig suit and see how high your morale and/or combat effectiveness is. Good luck eating at MOPP4. Not to mention the lingering effects of the "B" in NBC.
The NBC effects are not really modeled, but it's possible to reduce the faction 'training' and 'morale' levels in the battle launch options. That should be enough to simulate degraded unit performance.
No airborne units? Probably the only units that would have made it to Europe before it was all over would be the units on 18-hr "wheels up" missions (82nd Abn, 75 Ranger, and SF). 20,000 highly trained troops running amok in the WP rear areas is not trivial.
The Soviet side does have airborne units. I think having units dropped into battle is out of the scope of this game.