Desktop email client applications have been redheaded stepchildren since… oh, about the time Gmail emerged.
I have used Thunderbird when I had multiple active email accounts, or when I wanted to move my IMAP messages from one account to another*. But it’s been all but neglected since… oh, about the time Gmail emerged, so it’s just never going to be my interface of choice..
By and large I’m a webmail guy now, using FastMail because Outlook.com and the rest are too Lowest Common Denominator for how I want to manage my email. And when I need to offload messages altogether, FastMail’s process is the easiest I’ve found for exporting those messages I deem worth saving.
*I can’t do POP mail because I have multiple devices for accessing mail — it’s IMAP or webmail, or nothing.