I agree that "reinventing" email, or building a business based on "AI features" are both terrible ideas.
We began building Marco not to do either of these things, but simply because _there wasn't_ any actual cross-platform IMAP client.
Apple Mail exists (but is terrible) if you only have Apple devices. Lots of other options like Superhuman and Shortwave exist, but only support Gmail+Outlook.
All we're doing is building the app that should have existed 10 years ago: a cross-platform, offline-first "Thunderbird". Except far more lightweight and modern. And yes, we've built it from the ground up. And no, it's not Electron.