I miss Pine too. I could read/file/delete scores of plaintext emails in seconds using single keystrokes.
Every email client I've used since Pine has been better at dealing with all the stuff we've bolted on to email (HTML, attachments, calendar invites...) but none of them have been as efficient at the core tasks of email as Pine was.
You could give my email client https://github.com/d99kris/nmail a shot. It does basic html email parsing (leveraging w3m and pandoc) and its user interface is inspired by pine.
Gmail is not a real email client; it lacks basic commands such as mail bouncing. Perhaps worst of all, it has no concept of conversation threads, as I demonstrate here:
I miss pine.