but then I realised that same challenge would be infinitely more funny with folks who have atypical or horror OCs

This is due to the limitations of rendering right, it would be too much to try and load a real city's worth of residents and all their houses. But lets think outside of video game limitations and about what it would actually be like in one of those cities.

In the game, Diamond City has about 60 people in it, named and unnamed. (I believe.) But in the lore it is estimated that Diamond City has between 700 and 900 people.

That's a lot of people post apocalypse... but objectively its not many people at all. Diamond City by modern American standards wouldn't even be a city, but less than a 'small town'.

At only 700 to 900 people, Diamond City would suffer horribly from the 'small town' affect especially in a world with no telephones or internet, and your only contact outside is caravans and adventurers.

Everyone would know everyone. Everyone would be related or exes or friends or enemies. Everyone would know everyone else's business. It would be so hard to sneak around or do anything shady like theft or cheating or rebellious teen activities without getting caught by someone knows your mama on a first name basis.

Families and lineages would be important, they would have pulls and influences and connotations. There would be inherited jobs (my dad painted the wall, so now I paint the wall, and I'm gonna raise my kid to paint the wall) (side note, i totally headcanon Scarlet and Geneva as Abbot's daughters. Geneva is older in a similar age gap to Nat and Piper and Scarlet is her younger half sister.)

Small towns also love to gossip. And with a character like Piper Wright in town you know that town would have a wild and constantly running rumor mill from "Myrna is a synth" to "Moe Cronin is on buffout" to "Vadim Bobrov cuts his moonshine with vodka" always evolving rumors that 99% of the time don't stick for more than a couple days.

“Freedom”