As you might have noticed if you use legends viewer a lot (or conduct raids, or play Adventurer mode), the villains update brought with itself a whole new array of irritating bugs; almost every visitor is part of a conspiracy, and site populations get bloated with outcasts that eventually outnumber regular citizens in a civilization. I don't know how much other people care about this stuff, but I like generating long history worlds and then not have my computer melt when I enter a human town because of "outcasts" that, according to other players' experiences, don't even exist in the game world and vanish from the site populations once you visit the site in Adv mode.
After messing around with the various site types, site caps and even modifying every entity so that they spawn a single site and never expand, I have come to the conclusion that historical figures just spam schemes and criminal organizations like there's no tomorrow, and there is no cap to the population of a criminal organization, causing a bizzare feedback loop. Normal citizens turn into outlaws, and since outlaws don't count for site population limits, the site replenishes its population and reaches the cap once again. Then, the outlaw entity absorbs more citizens, and the cycle repeats until you end world-gen.
If you don't want to wait for the next update and this bothers you, then the most convenient solution is to change the 'Population Cap After Civ Creation' value to a number much lower than the default in Advanced World Generation. This setting is not a hard cap on civ population, in fact I don't know what it even does exactly. Human cities will still boast sizable populations if you let time pass, wars and sieges will still occur just fine, and world-gen doesn't slow down to a crawl after a few hundred years.
As an example, the default value for 'Pop Cap After Civ Creation' on a medium region is really high (5000 IIRC, but maybe even more). With that setting, human outlaws start to outnumber regular denizens in Hamlet sites by around year 300. With the value set to 100, history generation is much faster and outlaws no longer make up over half of the world's population, not to mention that civilized populations also stay at much more manageable levels. I recommend changing the value incrementally, a value of 100 might be too low for you if you have lots of titans/megabeasts/necroes.
If this solution has already been discussed on these forums, then I'm sorry. I suck at finding old threads.