In what ways is Shipyard better and worse than Legion for game development?
Since no one here seems to have the relevant knowledge of both ecs crates, what about making an issue on one of the repositories asking for a comparison?
Crate authors have in general been willing to do this kind of thing before - for example, the author of specs wrote a pretty detailed blog post comparing specs with legion.
Or if they aren't inclined to do that, have you looked through the crates' READMEs for examples? I can't seem to find any benchmarks for performance, but since both seem reasonably fast, how the two libraries are used could be a good deciding factor.
You might be interested in this blog post. I 100% agree with the conclusion.
Maybe implement a small project with one and the other and see which one you prefer.