The problem is, some of these folders are massive, and I definitely don’t want to download them onto my Mac first — there’s just not enough space, and the process would take forever. I’m hoping there’s a way to move everything directly from FTP to Google Drive without my computer acting as the middle point. Has anyone managed to do this in a cleaner way?

I had a similar situation when I was migrating data off an old FTP for a client. Downloading wasn’t realistic with the size of the files, so I looked into ways to connect google drive to ftp directly. What worked for me was setting them up side by side in Finder so I could move folders between them without storing anything locally. It handled big transfers smoothly, and I didn’t have to babysit the process like I usually do with manual uploads.