What is the crowd's opinion of MultiPar?

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Along those lines is multipar which can use CUDA if you have a Nvidia GPU. Rather large speed increase.

I use that before I burn content onto (DVD/BD recordable) disk for backup purposes.

Never seen that behavior before, but I rarely use QuickPar any more. I would suggest trying MultiPar instead of QuickPar. QuickPar has not been updated in a long, long time.

The way I sometimes do it is archive with 7z (or even zip) into multiple manageable parts, with or without compression, then par it with multipar in a similar way of a RAID setup, creating parity to recover up to a specific number of corrupted files. e.g: 10 parts, be able to recover the entire set up to 4 parts being corrupted.

You can also look into snapraid. While most of the use cases is to point it to the root of a drive, I think pointing it to a folder(s) would work just fine (may be wrong), since it's file-based, while dropping the parity file into another drive for resilience, unless that has changed.

If you just want 1-to-1 or 100% recovery, I would do a mirror of the set and create a checksum file. Store one copy of the checksum with the original file(s), then another somewhere else. Or you could also do doing binary comparisons every once in a while. For checksumming I used to use: https://corz.org/windows/software/checksum/

Regarding PAR, I think the PAR2 algorithm may be old, but multipar is still being maintained (latest 1.3.1.1 in github). Not to mention the widespread use in usenet.
https://hp.vector.co.jp/authors/VA021385/
https://github.com/Yutaka-Sawada/MultiPar

Check out MultiPar. (It's Windows, sorry.) It can check and repair files. I use it at 10% when writing to BDs.

I presume it can run under macOS with an emulator, don't know of a direct port.

Something I didn't realise was that multipar.eu is a spammer site. The correct place is https://hp.vector.co.jp/authors/VA021385/ or the official forum https://www.livebusinesschat.com/smf/index.php?board=396.0