Zstd achieves considerably higher compression on some kinds of data with little to no preprocessing. LZ4 hits a compression ratio ceiling at some point - algorithmically, it's "half of Zstd" (only LZ match/literal encoding, no entropy encoding at all).
Read the LZ4 format, it's very simple and educational, I'd say beautiful. It fits in half a screen of text.
zstd 1.4.5 --fast=5 2.178 700 MB/s 2420 MB/s
lz4 1.9.2 2.101 740 MB/s 4530 MB/s