I write ~35 GB almost every day when backing up. Once every 1-2 weeks I write over 600GB.
Absolutely - they should buy a mechanical drive. All of my backups write to HDDs for this very reason.
That's why I smile when people say they've gone "all SSD". Unless they're writing to cloud at floppy disk transfer rates, they're either not backing things up, or they're chewing through their NAND durability.