If you do such a gmail backup, I wrote a cross platform Desktop app that can analyze these email backups to provide a visual clustering of the contents of your mails.
I've been using Netviel (a web based not much client) to do this currently and it's annoying to have to convert my mbox files to Maildir to get it working. Thanks for posting!
https://github.com/terhechte/postsack
It parses 500k mails in < 1 Minute, so it is quite fast. There's a web / wasm build of the UI here: https://terhech.de/web_demo/