No. Having the same culture lowers revolt risk and increases productivity, and cultural nations can't revolt there anymore. It DEFINITELY represents a conversion of population, because if you conquered Genoa and made it French in the top strata, the city would STILL revolt. But it doesn't.
Sorry but you put 2 and 2 together, and end up with abstract numbers. There is no correlation between lowered revolt risk/increased productivity and a causality with conversion of population.
For African countries, again, it's just a show of force. People are not going to rebel and will work better once you show them you're are gods compared to them. In-game, the culture swap for these countries, to me, represent that. Couple thousands people on the coast to secure the trade zones, period.
For other countries, you can see it as a combination of diplomatic, administrative and militaristic presence. If you take Genoa and "make it French", you don't swap the population, but instead install French administration, French schools, French art and propaganda as well as make deals with local power figures so that they work for you. Genoa's been in the core Europe for like...forever. There is barely any difference between cultures and, again, apart from specific events, there is no reason as to why they would revolt, it'd be totally stupid. The population pays taxes as they did before, the nobles have advantages as they did before, merchants make money as they did before, etc...Apart from hardcore nationalists, nobody gives a shit and nobody's stupid enough to rebel against a country like France (apart from specific events, as said). The era of "peasant rebellions" is over and done, this is not CK2.
Heck, a couple years after you swap and core, any other nation could just take it from you and do the EXACT SAME thing. NOBODY CARES, it's all the same anyway. Europe has been in a Feudal system for hundreds of years at that point, with counties changing hands every year or so. The concept of "nations" is just starting in that period but it was still very fluid.
Only by 1700s and onward you'll really get widespread hardcore nationals. And even then, look at the Napoleon era. France "culture swapped" nearly all Europe in years with improved administration, schooling system and militaristic organization. Nearly all western Europe legal and administrative system is still more Napoleon French than anything else today. That only took a couple years and you didn't see "rebellions"...
My point is that you can't take the concept of "Cultural swap" and "Coring" literally. They are symbolic representation relevant to their historical context only. Swapping culture means you control it's administration, trade, diplomacy,etc. Coring means you identify it as yours in the circle of Nations so other nations don't fuck with you. That's all.
Now, play as Timurids, get Genoa and try swapping/coring/converting: Good luck with that...Heck, it takes years just to swap cultures they already accept in their own core territories
With all that said, this only works if you have enough events to simulate specific issues or it'll get "easy" and boring quite fast, I agree. I don't have enough varied playtime in EU4 yet to answer that, but even if it's not the case, Mods can very easily solve any issues left over.
