None of these mechanics make any sense, especially when Imperator: Rome exists.
In that, you have pops like Victoria (just without jobs, pops of certain classes produce certain general resources, sort of like just having an RGO instead of occupations). You have five classes; Nobles (your researchers/generals/governors/etc), Citizens (your voting bloc and where you get tax money), Freemen (producers, very little unrest but not the most productive), Slaves (high unrest, very limited assimilation, but good productivity and low upkeep) and Tribesmen (representing the rural barbarians, very limited production, no taxes, but can fill out your army needs when given integration rights). Added on top was the state religion, which is what you use to pre-convert pops to your culture. All cultures can be set at certain rights they cannot go above, eg: Rome has Romans topped out at Nobles, Etruscans at Citizens, Greeks at Freemen, Gauls at Slaves or Tribesmen. Any in the culture can be any of the top class granted or any below, eg: you can have Roman slaves despite being a class with Noble privileges. If you want to convert pops to native cultures, you need to convert them to the state religion and then give their culture certain rights (eg: contracts, intermarriage) to speed it up.
Egypt starts with 5% of their pops as Macedonian, they cannot fill armies but they are your core of Nobles. Bohairic natives are given citizenship rights, so they cannot be converted to Macedonian unless they get supremely rich enough to acquire nobility, and most are not Hellenic but Kemetic in religion. You can create Macedonian ethnostate, but to do so is expensive and takes a lot of time, alongside pissing off the locals by reducing their class status to force assimilation. You must first bolster the Ptolemaic cult to get everyone to follow Hellenic Gods, then slowly convert the culture. The result is always a super state due to the size and the amount of happy pops, but the road to it is quite dangerous.
Vicky 3 is throwing this all out, I can only imagine so they don't piss anyone off because it's too close to modern day and black slaves aren't alien fungoid races (but slavery is still modeled obviously!). You should be able to determine which pops you want to support and which not to, it makes sense for a conservative Austria to bolster Hungarians to appease them and turn them against uniting with the Slavs, likewise once Austria-Hungary forms you should be interested in uplifting Poles in Galicia against the Slovaks. Liberal Americans should want to uplift blacks to counter the South's expansion, and the British should want to uplift the Irish to quell nationalism at home to help with foreign expansion. Instead, you're either xenophobic, xenophobic to anyone who isn't from the British isles, or anything goes. This game is just taking away options after options. No combat, no pop interactions, diplomacy is basically dead, worthless.