I'm not sure if it is hardware or drivers causing the crashes, it appears to be multiple causes for multiple issues. The laptop is three years old, there is no warranty.
The kernel panics are on a different laptop ('17 MBP) than the mail.app system instability issues ('14 RMBP).
Moving large volumes of mail has been a problem in mail.app for at least six years and remains a problem on both.
This is not normal and will be fixed under warranty like any other hardware defect.
> mail.app is a flaky mess as always. I added a fastmail account and my laptop became unusable until I removed it. Still no idea what that's about.
This is similarly not normal - possibly file corruption due to those panics?