A1. Preface - It is my opinion that loadout variety is a strong indicator of balance, and that a lack thereof is indicative of imbalance. Looking at the usage rates, we see diversity in high-slot module utilization. In essence, high-slot modules other than Shields (namely, precision enhancers, myofibs, damage amps) are seeing sufficiently high levels of usage to make the daily Top 10 every day. By contrast, 9 of the top 10 low-slot modules sold every day are brick-related, and the one non-brick module (KinCats) which makes the list just so happens to offset a penalty to stacking brick. In summary, when we look at daily high-slot module usage, we see balance; when we look at low-slot module usage, we see imbalance.

A2. Response - If we nerfed armor plates or introduced greater drawbacks to stacking them, mercs would be less inclined to stack brick and more inclined to run other things. There's a good chance we'd observe an increase in loadout diversity. If we buffed shields, on the other hand, there's a good chance we'd observe a decrease in loadout diversity as high-slot HP modules would potentially crowd out non-HP modules. In my estimation, a broader problem than Armor v Shield balance is at play here; that problem is the potential for HP Modules > All Else.

Agreed on all points. Though I would point out (in response to above) that Precision Enhancers routinely make the Top 10. Albeit barely; they're typically in the last position or two. This has been the case since December 2014.

7. Zaria Min Deir said so.

Regarding armour modules, I think the issue is not that they are overpowered compared to shields, but that there is a wider variety of good high slot modules.

In high slots, Myobifs and damage mods are both good and common, (though I think heavy damage mods should mirror light in %).

In low slots I can see why armour is preferred.
Shield regulators are only good at proto, and shield energisers aren't good enough to compliment them for many people to focus on a shield regen build.
Cardiac regulators are good but of limited use.
Kinetic catalysers are only really good at complex, and have huge fitting costs, particularly at lower tiers.
Codebreakers have ridiculous fitting costs for the benefit, and are only good at complex.
Range amps have been nerfed to oblivion. This also affects the viability of precision mods.
Profile dampeners are rarely useful on suits other than scouts due to the ever present danger that the enemy will field a Gal logi. The precision bonus should be replaced to allow more suits to fit for stealth if they wish.

High slot mods that need a buff:
Shield energisers/rechargers. They don't give enough benefit for the module sacrifice. Also, lower tiers are worthless.
Heavy damage mods. The Amarr sentinel is the most common because nobody cares that it only has one high slot. With decent damage mods a Gallente heavy would be much more viable, with the extra damage it could output.