Google Takeout is fine for me - it just gives you an .mbox file with literally everything and it can be imported into Thunderbird or Outlook.
Well this is what just a normal email client does - it downloads latest emails via IMAP.
That's why imap-backup is useful.
Lol that’s an email client! Not all email clients have a manual UI.
I'm confused -- Mbox files can indeed be viewed offline.
(Not to say your point about the ease of automating Takeout is not valid.)
But the crucial question is, can you use it after your account was automatically blocked? That's when I would acutally have an urgent need for it.
If you do this every year (I do it on Jan 1st as part of some other yearly reminders) then at most you lose 2 months of data (certainly not downplaying the gravity of that but it's better than everything).