It would be interesting to see some economics of what 8,000% increase in encoding time takes to make that money back in terms of storage or bandwidth. I also wonder how brotli/lzma would compare here. Are there some obscene modes on those that had similar results?
Far better, just like anything else based on arithmetic coding. The main distinction here is that the output can still be decompressed with a standard Inflate implementation.
This class of compression programs sees larger differences due to the way the data is modelled instead of the specific entropy coder used.
I once used https://github.com/google/riegeli and a low zstd compression level to store large quantities of protobuf data in an efficient manner (in terms of CPU, RAM and streaming to disk). Shame Riegeli is not well known, not well documented and does not have many tests.
It's entirely possible the degradation of their RTG power sources would be more expensive doing the compression then just sending the data as is.
And you're eating into a limited overall power and weight budget to do rather then say, run the science on the probe.