> a lot of research suggests that Classical Chinese is more similar to modern Cantonese This is often claimed, but usually starts by taking Mandarin as given,

> a lot of research suggests that Classical Chinese is more similar to modern Cantonese This is often claimed, but usually starts by taking Mandarin as given, then adding knowledge of Cantonese and observing that it allows reconstructing more features of Middle Chinese, like the final consonants -p, -t, -k. However, if you take Cantonese as given and then add knowledge of Mandarin, you can also reconstruct more features of Middle Chinese, such as the distinction between alveolar and retroflex initial consonants (s- vs. sh-). Neither Mandarin nor Cantonese is closer to Classical Chinese, the exact same amount of time has passed for both of them. Only when you combine knowledge from both, you can get closer to their common ancestor. The game of "my language is the most ancient" is a common pastime among language preservation activists (not just in China, you can also get Romance speakers to argue who is closer to Latin etc.) but I don't think it should be necessary. Languages are preserved by being used, and most people don't choose to speak whatever language they use because of how ancient it is, but because it allows them to communicate with other people.