I can also endorse the Evernote-backup program on GitHub. I use it once a week to pack up my Evernote database online. It creates and synchronizes with an SQL light database and each time you run it it does not repeat anything it only synchronizes what has changed since the last time you run the program.
After you have all of your notebooks exported which could take a few hours would this program but it would certainly be hands off. It runs by itself until it's done. A heck of a lot better than what you're doing one by one with a mouse.
Use either the Linux graphical interface or the Linux terminal interface to import your notes into Joplin cuz with the windows version of Joplin you can only import one notebook at a time. With the Linux and terminal versions you can import every notebook located in a single directory which is what you will have.
It'll take a long time to import everything but it will be doing it by itself. Still a lot faster than manually importing one notebook at a time.
One more important thing.
You will need this plugin for Joplin that this nice person just wrote. It takes all of the internal note to note links that will be orphaned in Joplin and converts them into links Joplin Style.
Without it you will lose all of your note to note links if you use them.