You're right, I don't object to any of those things, "quite" or not. I just object to people completely making stuff up. The truth matters!
Mixed casting for whatever reason - widen audience, increase diversity, modernise, make a point, is one thing.
Completely bullshitting that actually there were loads of people of all different ethnicities wandering around rural Hertfordshire in 1810 and nobody would have batted an eyelid is another, completely separate thing.
TV shows aren't real but racism is. If people start completely misrepresenting the truth it;
a) diminishes the actions of people who fought and in some cases died for better rights and representation
b) suggests to people who don't have wider historic knowledge that actually things weren't that bad - and that's a very slippery slope
"Those who don't learn from history are doomed to repeat it." How are people supposed to learn from history if people lie about what history was?
tl;dr I wasn't commenting on the representation of colour in the show, I was solely responding to the quoted poster's comment, which, in my view, consisted of two statements that were both inaccurate and, in terms of minimising lived experience of POC, borderline offensive (because while I don't know what the poster meant by "rabid" racism, to pretend someone of asian heritage living in the UK in the early 19th century wouldn't have faced what we consider to be significant racism is insulting).
I would have made exactly the same point if the poster had significantly misrepresented the reality of women, gay people, people with disabilities, etc. in the same time period.