Not to mention the part where adding compressors like this somewhat defeats the purpose of using a simple format like QOI (although at least zstd is faster than gzip, let alone 7zip).
But if we're modifying things like that, then they might as well make use of Nigel Tao's improved QOIR format, and replace the LZ4 compressor it uses with zstd. That's probably faster and likely compresses better than QOI.
So to clarify: my suggested point of comparison was replacing QOI + 7Zip of GP with QOIR + zstd. QOIR already compresses better than QOI before the LZ4 pass, and zstd compresses faster than 7zip and often better. On top of that you can put zstd in the header option when streaming data on a browser so you don't need to increase the JS bundle or whatever if the use case is the web. So that's basically a guaranteed net improvement all around.
Second of all, the speed/compression trade-off with zstd can be tuned a lot. The "half as fast as LZ4" stat is for the fastest setting, but for the proposed comparison point of 7zip a slower setting with better compression ratio is likely perfectly fine.
