The question is: how did your test reader respond to the version without the "It's not just an X, it's a Y." ? Perhaps the discussion went:
Test Reader: I got confused when you started talking about X as though it were a Y.
Author: But it is a Y. I should flag that up, where I introduce it.
Alternatively, the test reader comments
The villains monologue wasn't unhinged enough. He says that making himself universal dictator is democratic because he gives people what they secretly desire. I feel he would express himself with more empty rhetoric.
Author: Agreed. I'll add "It's not just democratic, it's not just super-democratic, it's ultra-democratic!!!"
Test Reader: Scary!
The error lies in using "It's not just an X it's a Y." for emphasis rather than to ward off a likely misreading.
Test Reader: I got confused when you started talking about X as though it were a Y.
Author: But it is a Y. I should flag that up, where I introduce it.
Alternatively, the test reader comments
The villains monologue wasn't unhinged enough. He says that making himself universal dictator is democratic because he gives people what they secretly desire. I feel he would express himself with more empty rhetoric.
Author: Agreed. I'll add "It's not just democratic, it's not just super-democratic, it's ultra-democratic!!!"
Test Reader: Scary!
The error lies in using "It's not just an X it's a Y." for emphasis rather than to ward off a likely misreading.