I think a big part of the problem is even if Takeout is using standard formats, none of their competing services or software platforms are set up to ingest thos

I think a big part of the problem is even if Takeout is using standard formats, none of their competing services or software platforms are set up to ingest those formats. Like mbox is fine for opening in a desktop client, but if you move from Gmail to Fastmail or Outlook or whatever, mbox might as well be a ClarisWorks spreadsheet file.