To add:
2: “other backup tools” confused me too. Most don’t just copy files directly. Got names? Sync tools would, however you lose lots, such as ability to get to old versions at all, or efficient storage of versions. Features shows several that would not be possibly with direct file copy, however there are definitely some tradeoffs.
4: Paths beyond the “normal way” include downloading directly from destination using any tool it supports, Duplicati.CommandLine.RecoveryTool.exe which is sometimes needed if the backup has been damaged. Independent restore program is a Python script without any of the normal Duplicati code.
Agree with prior answers to 3 and 5. There are likely more stable backups than Duplicati (still in Beta), but there are no perfect ones. I feel uneasy looking at this list, at all the complex questions it’s not considering. Possibly some further study of how to choose a backup program for your specific needs would be helpful.