They aren't represented even remotely properly if it's completely anachronistic. And the end result is that while most people roll their eyes, some still watch and others switch off. A minority of people get quite angry and it's very likely that in the mid-term aggressive racism will increase as a result. I can already see the beginnings of it, tbh. In the same way that there are genuine fears about a backlash against LGB people due to 'queer' activism. Constant race swapping of ethnically European characters and real historical figures is one of a number of current day race issues that could lead to a backlash.
British society has been just about the least racist society, possibly to ever exist, for the last decade or two. With most of the more recent large scale victims of institutionalised racism being Irish, especially Northern Irish Catholics, ie white, as a result of the civil war in Northern Ireland. But that has improved so much since the 90s. Britain isn't perfect but the vast majority of people, especially in major cities, which is where most of the ethnic diversity is, are more than happy to get along and share the best of each others cultures. And if anything is going to destroy that it's taking people's cultures.
Enid Blyton's books are something quintessentially English. A slice of a particular type of culture at a particular point in history. For example, the constant long descriptions of the food the children eat, is a result of the books being written during rationing. Eating tongue sandwiches, with a salad of fresh lettuce and juicy tomatoes and following that up with a thick slice of victorian sponge filled with lashings of cream and homemade jam, all washed down with a bottle of ginger beer, was a complete fantasy to children reading the books. Even for the middle class readers, just the idea of being able to eat simple but delicious foods on a regular basis was a distant memory for the oldest and something the younger children wouldn't remember. The adventure elements and the fact that children are so often alone without an adult, was especially in the earlier books, a reflection of the fact that many of the readers would have fathers at war and many would be away from their mothers due to evacuation from the cities. The books were both a simple escape from the realities of living through a war while also a reflection of children dealing with that stress.
As a non-British, non-middle class child who had never had to deal with rationing or the types of sexism that so influenced George and Anne's personalities, those books gave me an insight into a particular time and place. They let me identify with children who were nothing like me. And it's actually really, really fucking important that we all learn to identify with people despite our obvious differences. Only being able to identify with people who look like us and live lives like us, is exactly where problems start. Whereas being able to see people who are on the surface very different to us yet recognising our common humanity and identifying and empathising with them, is how we make humanity better and move forward as a species.