Slapping a low drop rate on something and calling it "done" is incredibly lazy game design in this day and age. SE have tried to not do it too often, for the reasons that have been mentioned in this thread. The backlash from Atma more than likely caused them to realise that people are sick and tired of being bent of over a RNG barrel for the sake of extending content/subs. Mirrors and Atma were some real Tanaka-channeling stuff straight out of the dark days of XI.

Totally agree with mirrors/mounts/atma being something you should be able to work towards over time. I might actually have some tangible reason to go back and do EX primals more often, seeing as they got outdated in a single patch cycle (seriously wtf is with that?). It might actually be compelling to work on the Animus bow if I didn't dread going through the RNG again with all of my being.