"I'm not sure why that story fits Doctor Who" is perhaps the saddest sentence I've ever read and contextualizes a lot of your comments.
To be fair, there is a logical thing here...Who rarely touches American History, (though it’s tinkeed with the settings lot more of late) and rarely touches the big things in history in general...and no pure historicals in some time, as the Rosa episode almost, but not quite, is. It also almost never touches what might be termed ‘modern’ history. Full on Second World War stuff doesn’t show up till Fenric, and I don’t think we see the Nazis till NuWho and let’s kill hitler. (Neo Nazis turn up in silver nemesis though.)
It’s always through allegory, or its distant past with its Aesop leanings.
The other thing...coming back to the American History aspect a little...is that Rosa and MLK is taught in schools as standard here in the UK, but it’s not *our* history, and who is still a British show. (Qualifier..I understand and acknowledge it’s place in world history, but every place on earth has its own history, and the history of other nations slots in in very different ways, so by our, I mean local essentially. I don’t downplay the events importance, nor how important it is as simply a way to show how bad things are, or how good people that stand up to them can be.) Demons works in a way that Rosa can’t....Demons ties to the modern companion, and to modern Britain.
So I can see how Rosa May not feel like the best fit for who, whilst personally not having much feeling myself in that manner, and without considering it in any way ‘lesser’ for that. (As it seemed either other poster.)
Who has tackled all sorts...South African apartheid, drug addiction, power structures, eastern philosophy, western, the EEC and through extension the EU, all sorts...for decades. But SF and Who have the power to use Allegory as a powerful tool, and rarely does it deal with the actual politics of the historical periods it uses as settings...Ghost Light for instance dabbles around a pot pourri of Victoriana, with its crown saxe coburgs and it’s naturalists, colonialists, and science and religion stuff...but it’s not ever directly dealing with actual events. Nor does it make much of a judgement, it asks you consider them, and talks about them again through allegory. And it’s a potent cocktail.
That’s what who does. It very very rarely just sits there so you can see some history happen...it’s not done that in a very very long time indeed. Part of the reason is that, particularly with modern history, it has always been wary of trivialising very important things, often in living memory, by using them as the backdrop for entertainment that is in the shows DNA. It’s why Rory punches Hitler and sticks him in a closet. Who deals with Hitler through its Helen A’s and it’s Davroses, when it’s actual Hitler, he’s a punchline. Because it’s almost someone else’s job to deal with that. And it skated on thin ice there...we all loved it in some ways, but there’s also a sense of ‘why did we just use the greatest evil (possibly, there are contenders after all for that title.) as a joke’ and some people were outright upset we didn’t see the Doctor deal with athat evil. (Something Rosa sort of addresses....we can’t see the Doctor deal with actual real world evils, because the Doctor is a fiction, it breaks the suspension of disbelief, and that’s hidden in the unpleasant idea that bad things are fixed points in time because that’s how we get to where we are today. It gets very mixed. Turning real history into alt history could be dangerous game depending how it’s handled. We were all worried how they would handle it. But it outright meant the one person who always saves the day, the hero of the show, of actually being able to save the day in a way they would have done on any fictional world. Tough sell. It kinda works.)
I watched people criticise Downfall, and say it shouldn’t be made, out of ideological belief that it somehow humanised Hitler. I had to point out the danger in that. Hitler isn’t a fantasy a monster, he was human. That’s where the real monsters come from. Believing they don’t is a fools errand, and blinds you to the possibility that could happen again. You can’t make real life too much a part of the fiction, and still have your hero save the day. It’s a very very fiddly game to play, particularly in a fiction me at at least in part for a young audience.