Disclaimer: This was not my idea. I came across it while reading old threads and decided that it had potential. This is my attempt to make it noticeable.
Iron Plates should have their weights halved to 20 kg, while PP stays at 40 kg. This means that although heavier, PP is more efficient as it is essentially 2 plates in one (and a little bit more). While not straight-out nerfing PP or buffing IP, I still think this a good way to find a compromise between them both.
PPs wouldn’t be so OP anymore, they’d just be more efficient. Plus, the extra weight could provide room for more weapons/modules to make up the gap between IP and PP.
The same could be applied for resistance mods.