Where Zstd will reduce, say, 3x, Lz4 reduces only 2.5x. This doesn't seem very different until you look at it from the other end: my .zst file is 3.3 GB, but the .lz4 would have been 4 GB, which is 700 MB more.

Was a time when 700 MB mattered; it was as much as you could get onto a CD.

So, there is a place for each. I would set up the process to use Lz4 when testing, and Zstd for actual delivery to download archives.

In some circumstances, particularly when using a shared file server, Lz4 can be quite a lot faster than writing and reading data uncompressed.

Guessing that 0.8x size increase for 1300% speedup was worth the tradeoff but maybe ≥1.5 size increase or more was not (especially considering a 1300%->2000% increase is not going to be user visible for 99% of the packages).