This r/korean comment answers my question as "yes", but it contains factual errors like "Cantonese is also much closer to Middle Chinese than Mandarin is". This r/linguistics comment and Quora contend that Korean share more phones (or phonemes — which is the correct term?) with Cantonese than Mandarin. Can someone critique that comment please? Any other errors?
Q: Is Cantonese closer to Middle or Old Chinese than Mandarin?
A: The general answer is NO, since both languages have undergone a lot of change. Phonetically speaking, certain aspects of the Cantonese sound system have undergone less changes than Mandarin has, so in those respects, it would be closer. Nevertheless, Middle Chinese pronunciation is still a long way from Cantonese pronunciation. Certain vocabulary has been preserved, while others have not. Grammatically, there are definitely differences. If you traced the two dialects back to Middle Chinese, you will find that both have undergone significant change.