Choice of compressors seems to be suboptimal
The latest tor-devel uses 2 compression libraries: zstd and lzma.
Based on this graph https://raw.githubusercontent.com/facebook/zstd/dev/doc/images/DCspeed5.png lzma only slightly exceeds zstd in a small range of values.
Why didn't you choose lz4? Based on this lz4 description https://github.com/lz4/lz4 it offers an advantage in a different range of values: towards the lower left corner of the first graph. lz4 can compress with lower ratio but with much higher speed.
If you want to choose several libraries, doesn't it make sense to cover a wider range of values, rather than choose two libraries that cover a similar range?
zstd + lz4 seems to be a better choice.