Interesting, that's kind of surprising. Do you mind sharing which model of MacBook Pro it was? I had been considering getting one for cheap for testing purposes. Also, it may not be useful to you at this point, but I figured I'd drop a link to the Debian Wiki which has a page for MBP-specific info, in case anyone reading might benefit: https://wiki.debian.org/MacBookPro
Non-free-firmware is now handled automatically during installation as of the most recent Debian release, just FYI. For reference, see the note at the top of this wiki page: https://wiki.debian.org/Firmware