How is this compared to other ecosystems? I've been serializing JSON for about a decade and it's been so fast I haven't really thought about it. Simdjson can do gigabytes per second per core.

Once you factor in prefetching, branch prediction, etc., a highly optimized JSON serializer should be effectively free for most real world workloads.

The part where json sucks is IO overhead when modifying blobs. It doesn't matter how fast your serializer is if you have to push 100 megabytes to block storage every time a user changes a boolean preference.