The Apple-II cassette interface is simple, fast, and I think most reliable. The data transfer rate averages over 180 bytes per second, and the recording scheme is compatible with the interface used with the Apple- I. Note that this is almost as fast as the floppy disk drive on the Commodore 64. This is why people remember Woz but not the anonymous engineer(s) behind the 1541 disk drive.
Wow, I used the 1541 for backups in one job. I never timed it, but I'm not surprised at your report.