"degrade or are obsolete (both form and file format) after a few decades have passed"
Some film and prints do too. While well developed B/W films and prints could become quite stable, many colour films were not especially until the 1980s - and there could be still issues.
It is true it could be easier to recover a negative with a big colour shift than trying to get back an image from an old floppy disk or ancient disk driver, or a damaged CD.
Don't know if M-disc can become really a good long-term storage medium - that depends on the availability of readers in the future.
Biting the hand that feeds IT
