Making it binary instead of a scaling bonus/malus is a bad idea because you get into silly situations where 0.5 armor or 0.5 piercing makes an enormous difference in combat effectiveness.
This is a bit contradictory. The first is not silly as armor against an opponent with too low piercing to deal with armor frontally is going to be in trouble and will have to spend considerable combat effort to crack those AFVs. Mobility kills, mines, artillery, grenades etc also count but are not as effective. Not being able to pierce your opponent effectively means you're always forced to fight in a certain way (unless you're stupid but then you'll lose).
Even light armor will maul infantry with no AT and their ability to fight off an armored opponent instead relies on terrain and tactics. That said, with handheld AT (mines, AT rifles, bazookas etc later on) you still have a decent ability to be successful but you're still forced to adapt so the 50% damage reduction is not over the top (and you still get to use a lot of your SA against opponents with low hardness).
Likewise - the combat effectiveness of full LARM/ARM/MEC divisions lose a big advantage that they really should have because a division has a support AT company - even though that amount of guns would make virtually no difference IRL. (A US infantry division had ~100 because it became obvious very early in the war AT was so important)
Counting AT guns (not bazookas and everything that goes under the infantry-tree but rather AT gun production and units) a US Infantry division had 57 AT guns.
An in-game division with 1 line AT and one support has 60.
A fully armored division that faces an opponent with AT weapons that can pierce its armor effectively is restricted to operating with that fact in regard. After the first few vehicles are knocked out they won't start a slugging match but instead chose another approach.
That on the other hand comes down to commanders skill, doctrines, experience etc and that's an area where the game is lacking. The combat "tactics" that are picked could be a lot more evolved to handle such situations depending on experience and doctrines.
I would like to see tactics that affect certain modifiers as that's basically what tactics are all about, making the best use of the equipment and manpower you have.
Ideally we would have combat tactics that enables an experienced division trained and operating under certain doctrines along with an experienced commander to not stonewall themselves against fierce armored and piercing opposition (say PzII/ IIIs vs Char B1s) but instead utilizes armored infiltration tactics, CAS (basically just hold and let CAS pound the baseline), flanking etc etc that modifies the modifiers. This is something I'm hoping for in future expansions or at least as modding support.
People should need to actually put effort into AT if they're going to be facing armor divisions.
You do because you need to get your HA up. Against high hardness divisions (ie not TD/INF) you need high HA and that's very hard to accomplish without large amounts of AT (piercing or not).
I don't care if obsolete AT can pierce LARM but you need to have enough of it. You're belief that 24 over a whole division is enough is not only wrong but contrary to the conclusions reached by the people actually fighting WW2 who felt 24 was very much too small.
Soldiers ALWAYS thinks there's too little hardware available, believe me. And it's true, you can never get enough stuff, but you make due.
That nice hill with good fields of fire for the infantry might not be as attractive if you only have enough AT to cover the road embankment and various village streets. You'll be forced to place that battalion elsewhere where they won't get mauled by armor, mine the place up and just leave a section of engineers and a FOB team (just as an example why you get penalties to the attack stats).
24 guns is better than no guns and they will be put to use where they are most needed, either overlooking channelizing terrain or/if where there is none (in order to force the armor to chose another route, preferably into prepared positions or channelizing terrain). Of course the more the merrier but there's no specific breaking point IRL, it just puts restrictions on how and how much you can utilize the rest of your force and thus the different armor modifiers are, IMO, not over the top.
All that said there's room for improvement and I personally would've gone about the combat mechanics in a different way. But then I'm not a game designer and the actual results that you get on-map with two divisions in combat is not wholly improbable.
