Gmail All Mail Label is now mapped to Archive in Mail.
Gmail isn't IMAP, though it tries to pretend that it is.
Gmail doesn't have folders/mailboxes or anything like them.
It "tags" messages with Labels. When an email arrives, it is tagged with an "Inbox" label and an "All Mail" label. Mail attempts to resolve the "same message exists in two different folders" conundrum that doesn't exist on IMAP.
"Important" is another label. So, an incoming message could exist in three folders. Dogs and cats, living together.
In Gmail settings, Labels, you can tell it to not show the All Mail label in IMAP, but that doesn't stop it from collecting everything you've sent or received, even if you delete it, in All Mail. It just prevents you from seeing it in an IMAP email client like Mail.