I typically don't make use of standard archive formats these days for my own file storage. If I want just pure maximum compression, I'll often use a long-range matcher like FreeArc's srep [1] or lrzip [2] combined with either fast-lzma2 [3] using a p7zip fork [4] for multithreading and fast compression or use mcm [5] or zpaq for max ratio with longer compression time.
However, my truly preferred way is using dwarfs [6], which features some really good deduplication and (by default) zstd compression while being mountable. Most of my files are highly compressed and easily accessible without needing to full decompress them. I even made a small script to convert and create AppImages that instead use this [7]. Admittedly, I don't make use of PAR2 or anything of the sort, but I could just do that the traditional way if I so wished.
[1]: https://github.com/Phantop/srep
[2]: https://github.com/ckolivas/lrzip
[3]: https://github.com/conor42/fast-lzma2
[4]: https://github.com/jinfeihan57/p7zip
[5]: https://github.com/mathieuchartier/mcm