I guess the main character of OFAHl is South Africa.
I think the nature of timelines that cover more than 20 years is it makes it much harder to have a single main character you follow, which adds an extra hurdle to finding an audience outside of niche forums like this.
The classic expanded presidential list has like 30 rotating main characters, essentially. And that makes it harder, cos once you sell the reader on the struggles of one guy, he's quickly gone and you have someone else to deal with, so there's no emotional connection. Which is why that format only really works with known historical characters where the audience already knows who Thatcher or Reagan are and get what it means when they arrive on stage.
Like you say the other way you deal with that is to make the setting what the readers are attached to, which is also what mainstream authors of like soap operas or generational novels or fantasy settings do, where characters come and go but it's the street you're following.
But even most of them have anchor characters who work to transition from one generation to another. I think one of the things I'm unsatisfied about 'history of the true whigs' is I didn't have that in the modern day the way that Blyden and Garvey cast their shadows over the early bits, which meant it quickly just became 'here's a person' with no greater connection between them and it just kind of ended rather than climaxed.
But then timelines aren't often stories and I think the best way to get a story out of a timeline is simply to narrow it down on a time period and write one there with the setting as background. As the key for a good story is often a good main character you can follow and you can't really do that if you're starting 200 years after you finish.
But then there's always the argument that people who like stories aren't really looking for stories about early 20th century African politics and people who are interested in those politics aren't looking for stories.