The thing I don't understand about the (let's call it) simulationist argument is that it seems they do not want there to be the freedom to do whatever you want with your army, rather than simply altering the game to a point where certain strategies are not be as effective as they are now.
You'll still have the freedom to do whatever you want with it. You just shouldn't expect some things to work consistently. The hard part of trying to explain the simulationist model is that it is almost infinitely complex, based on combined arms and co-ordination between different arms. Teamwork is mandatory for success. It's roughly as big a leap from Wargame as it currently is to the model we'd like to have as it is from Starcraft to Wargame. I'll give it a shot anyway.
The "typical" battle (whatever that is) would flow something like this:
Recon elements from both sides meet and airborne troops reach their objectives. Tanks and other heavy elements of the army are moving to support. There's a brief skirmish phase between the recon units as they joust for information supremacy; whoever destroys or drives off the opposing recon has an advantage in the upcoming fight. Airborne may have to fight to clear their objective. Tanks reach the main battle and deploy to attack/counter-attack. Front line, such as there ever was, is subject to artillery bombardment; finding and destroying the concentration of enemy reserve with artillery is a primary goal.
While this is going on, light elements and airborne try to hold strategically valuable areas and hit targets of opportunity. Gunships constantly run missions against enemy armor while their losses mount. Artillery has to divide attention between too many fire missions at front and counter-battery task while relocating every now and then to avoid enemy attention. Infantry digs in to hold the ground gained. All this beats in the rhythm of clogged roadways and supply units trying to support every combat arm. And then there's the enemy and his plans, of course.
To answer your worries about difficulty of attacking, it should be as easy as anything else (ie. not easy at all). Large concentrations of units fall prey to overwhelming fire support, so the front line must by necessity be lightly manned. Pushing through light screen of recon elements with armored battalions is not hard. The problems only start when the defender sees your main axis of advance and starts his counter-attack to drive you back. Essentially it's two sides attacking each other at once.
Even if you play this for simulation, surely your opponent must have the freedom to do the dumbest and cheesiest of things.
Yes. But should they work consistently? Anything can work once, I'll give you that.