Besides the producing one product this is not how the system works in game. The militancy, needs and every other stat are a % of the whole POP group.
It is like a sample group not every one of them is the same. Meaning if they are 5% liberal doesn't mean every one of the member of that group is 5% liberal. It means that 5% of that group a re liberal. The same with rebels.
A POP gets 40% of it's needs == every single one of those 50k gets his needs 40% fulfilled. Which means they all get pissed off. And yes, the militancy is a scale, but it is not capped. The entire POP becomes a potential revolter, even though logic dictates there should be at least some artisans who are doing good for themselves. Then again every single one of them produces exactly the same product, so who knows.

And if you butcher them when they rise up, it doesn't actually matter, because those rebels weren't the ones worst off in the group - because there AREN'T any worse off people in this POP.
There are other problems as well, of course, for example your country can have millions of soldiers while not having a single military unit, utterly mind-boggling province population make-ups (40% clergy, 30% soldiers etc

), the fact that people outside of the of the POP categories don't exist (where is the entire services sector, for example?

), the weird chicked/egg dilemma in case of capitalists and factories, the overall weirdness going on in the colonies etc etc.
Many of those problems are small ones, at worst requiring a balance patch, otherwise hurting perhaps the immersion factor only, sure. But POPs ARE rigid and inflexible, and I hope PDS finds a way to improve them in time for Vicky3.

They certainly DID improve the concept from V1 to V2.