The way armor works is too RNG in Path of Exile
Problem with all these other forms of defense is that you no longer really need armor or evasion. You can run big Energy shield, and still have all those layers around for defense. Why would you run Armor or Evasion when you can run double or triple the 'life' pool?
Another good question: Why would you run armor when you can run all those other layers, which are far more effective phys mitigation than armor could ever be? Going armor is a joke compared to Energy shield, because the way armor works is too RNG (not to mention how much investment you need to actually make it work well). Make it flat phys DR instead, and it would work a lot better.
The real problem is that when you make a build it centers on doing 1 thing really well. You can't have almost any bad map mods when builds are centered around one thing. It would make more sense to somehow allow characters to build around 2 things, maybe a primary and a secondary. Then they could work the primary unless they get a debilitating map mod, and then they use the secondary.
The problem isn't really map mods. The problem is that armor and evasion are not even close to as good as having a giant 'life' pool. Armor and evasion are too RNG. With Energy shield you always have that giant 'life' pool. It's consistent. Plus you can still get tons of defense from other sources, as mentioned. If there were less other sources armor and evasion would be more worthwhile.

Nov
This means you now have legacy items
What you're thinking of is something along the lines of Legendaries from other games, which are the super GG items that have no better equivalent and are very rare.

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