But your examples are more about the show just wanting to continue to reflect the modern day
But that's part of the problem with that genre of story. They're just trying to conform to the real-world reality, but they're arguing that there are no better alternatives, that the world we have now is the "right" one even if millions of people suffered and died to produce it. And given how many of those people who suffered were minorities or working-class people, that's really a reprehensible mentality when you look at it from their perspective.
It's also completely arbitrary that in any time-travel story set in the future, it's perfectly okay to erase a dystopian future and replace it with a better one, but if it's set in our past, it's completely unacceptable to change even the worst parts of our own history. It just exposes the artificiality of it as a storytelling device.
Not that there haven't been good stories using the device -- "The City on the Edge of Forever" is a standout example, of course -- but I think it's overused, and it's worse when it's saying a major disaster with many victims "has" to happen, or that a war has to happen or a whole group has to remain oppressed.
And hasn't the Doctor working to ensure that major historical events have always played the way they were originally recorded been a big part of the show's historical episodes all along?
Not really. Most of the historical episodes in the classic series didn't worry much about the temporal paradoxes and such. There were a few that addressed it; "The Aztecs" had the Doctor tell Barbara definitively that "History cannot be changed, not one line" -- not "should not" but "
can not," an immutable-timeline model -- but then "The Time Meddler" contradicted that and they had to stop a rival Time Lord from altering history. But usually that wasn't an issue, because nobody was trying to change anything and so nobody had to worry about the question. They just got involved with events and watched them unfold. Usually they were just on the periphery of the big events and trying to find each other or escape captivity or whatever, so they didn't have much chance of influencing the major stuff. Or they were involved with people not recorded in the history books (like Jamie) and thus didn't know what would happen to them one way or the other. "The Massacre of St. Bartholomew's Eve" ended with the Doctor and Steven having a falling-out over the ethics of letting a historical horror play out unchanged, but not until after they'd already left that era, and it was the exception, not the rule.
After all, the goal of the early historicals was to teach children history by dramatizing past events, so they wanted to depict them relatively accurately and just have the main characters be spectators. The focus was on showing what happened, or on depicting a culture and period, not getting into timey-wimey paradox stories.