First, change Gmail advanced settings from archive to delete.
Then, in mail swipe settings, correctly interpret these baroque directions: “Accounts that include Archive as a default action for swiping left will offer Trash for swiping right.”
Then in Swipe Left settings chose Move Message.
Then in Mail.app when browsing swipe right archives and swipe left deletes.
There’s more broken stuff like this in iOS. Articles on “new features in iOS 11” irritate me. There’s a lot of unfinished work in iOS 10.3.