however, because they lack the training and displine to properly brace themselfs for attacks by heavier forms of cavalry. Notice they don't plant their spear in the ground, and they only hold them WITH ONE HAND. That is why I feel they should largely get busted by heavy cav.
Two points here.

One, ALL spear units, (including Papal Guard, who are the best), use spears in EXACTLY the same way as Spear Militia. They ALL carry their spears in one hand, and NONE of them stick them in the ground.

Second, Spear Militia, ARE NOT peasants given spears and shields and shown how to use them, that’s Town Militia (who only get Light_Spears and Spear_Bonous 4), Spear Militia represent professional militia unit. Individuals given equipment just below the level of professional soldiers and the best training that can be given to Militia level units. Italian Spear Militia, (and similar top level Militia units), are better more because of better equipment, they actually have professional equipment instead of high quality Militia equipment.

NOTE: the above may or may not be historically accurate, but it IS how they are portrayed in game, and that’s what I really worry about as it shows designer intent IMHO.

My point on schiltroms is that it doesn't work that way in the game. The arrow trajectories in the game mean that half or more of your arrows are going over the guys facing you and striking the guys facing the other direction in the rear or sides...
This isn't actually as common as you'd think and comes with disadvantages. On small size at least, most arrows that would not hit someone with a shield will simply skim right over the unit. Larger unit sizes will probably result in the arrow hitting the shields as their more rank for it to fall into. Some will of course hit them in the back AND if you do really big angles on the arcing fire then YES you will get them hitting guys in the back, but your sacrificing a lot of hitting power to get that kind of angle, (it also won't work with Crossbow units at all, gunpowder being powerful enough to not care about the shield).

Don't get me wrong, the current shield fix does bork things, but in my experience, short range arrow volleys are too flat a trajectory to hit the unit without hitting a shield more often than the hit someone in the back. less flat trajectories introduce problems with reduced impact power. Their IS a perfect position I’m sure, but it's probably not easy to judge and get right.

Don't get me wrong, Schilstrom IS a LOT more resistant to missile fire ATM, but I don't think the difference will be quite as large as you think it will be either. In the end I think we should just wait and see.

To those worried about late era units getting wailed upon by early era units. I would point out that most good late era infantry is AP 2-handers and pikes. Even with the Shield immunity to AP back in, the shield units will be at a heavy disadvantage to them, so they won't be getting any weaker really. They also typically have much of the shield value dumped into armour anyway. This will make them a lot more resistant to enfidle fire, and hence HA anyway. (At least in the case of mounted units,. Late era Inf tends to be more vulnerable).