I think a good backup is most important for data you don't want to lose. I think redundancy is more about availability and getting back to a working state faster. With RAID 5 you lose a drive. The data is still on the other drives so it is just a matter of putting in new disk and rebuilding the RAID.
Some of you might be interested in this:
How to share your data across Drives with symlinks and no pooling.
Part of it comes to level of convenience and likely failures.
Given that (in my case) this is all replaceable media, backup isn't necessary. My blurays and the Internet are the backup.
The most common problem at this point is single drive failure, and raid will handle that.
So raid 5 will let you survive a single failure without requiring huge amounts of space for backup, only sacrificing a single drive of space. The work to replace the lost drive is also less than if I used jbod and had to rerip or redownload the contents.