I would rather be able to see statistics about the domains of the email I receive instead, to see offenders etc. I already created a lot of filters for that, which helps a lot do some cleanup.

Also, I seem to have a lot of attachments, like a lot, and I can't clean them up, because gmail doesn't let me see the datasize clearly.

I downloaded my mail as an export, I think EML, I wanted to build a mail list myself to see attachments with a python script, but I think gmail doesn't export all the metadata of how mail are chained with each other and such.

Unfortunately, I think your extension cannot really do statistics on an existing mailbox, to see a map of mail counts per domain.