Earlier quoted context omitted.
Here's a few things: - constantly changing things around. UI gets less intuitive for every release. - slower for every release - violates IMAP standard by re-using IDs across tags/IMAP folders, risking actual data loss. Example: if you in a real email-client try to delete a email from a single folder, you will also delete this email from all other folders it has been "tagged" in. - similar IMAP issues with sent email…
The messed up deletion behavior baffles me to this day. The stock mail app on iOS will behave correctly if you muck with the Gmail POP/IMAP settings and turn off 'Archive' in MobileMail, but I have zero confidence that this will work on macOS because Apple pays less attention to the desktop and Gmail don't give a crap if actual client applications work correctly. They just assume everyone uses the web interface.
More likely, they want you using their app and their web interface, and merely tolerate third party apps. For now.
Google wants you in the Googleverse forever.