This could potentially be problematic. If you mix just a few of them into pure militias you get militia with 3/3 armor. Basically a combination of Teuton and Malian militia bonusses. Even halbs would get a boost against skirms, taking 2 less damage per shot.
This would basically allow any civ to make a goth-like army comp. Ofc not usable in the same way as goths do it with their flood, but it would still be a very potent combo that would be really hard to deal without any specific infantry counter like HC.
You potentially also could just mix in a few of them in the defensive mode into most of them in the attack mode. Imagine these things in the attack mode but with 2/2 armor…
I personally would prefer if this has only one mode, the defensive one. But instead of giving the units around pierce armor, it has just very high pierce armor itself and the Hussite Wagon ability of reducing the damage dealt to units behind.
So you can use it to soak arrowfire against your vulnerable other units. This way you would need to costantly reposition the Shieldbearers to get the desired effect.
I’m also not too sure if I want to give them more PA or more HP. I think more HP is potentially better. Giving them too much PA would make them essentially just an Archer counter which in my opinion defies the general counter wheel mechanics. Then a mix of these plus Pikes would beat basically kill the whole Knight/Archer meta. Imo it would potentially be sufficient if they had like 2 pierce armor but 90-100 HP. This way they would especially excel against Skirms but be less effective against archers.
In the aftermath this unit wouldn’t be a “Power Unit” but rather a tool to protect your own trash units better against the counters of the opponent. It can help pikes against skirms and skirms agains cavalry, even light cav against pikes.
So not a real “power unit” but a nice unit to increase the diversity and dynamic of the already established power unit matchups.