The amount of thought and awareness that goes into the experience of corresponding by letters seems like a bit of a lost "art" today.
(Theodore Roosevelt's 1903 State of the Union speech had a Flesch-Kinkaid score of 15,1. But then again, apparently even Queen Elizabeth's christmas messages have become measurably less posh over her lifetime)
https://www.theguardian.com/world/interactive/2013/feb/12/st...
To be clear, her reduced 'poshness' is due to changes in her pronunciation over the years, not the content or reading age required. She has moved to a more generic southern English accent rather than the 'cut glass' accent of the upper classes when she was born, in which 'house' would be pronounced 'hice' and 'trousers' as 'trizers'.