I think that's a really good point, and I definitely agree that rkyv, Cap'n Proto, and FlatBuffers all have different goals and design decisions. rkyv was primarily made with the intention of handling bulk structured data for game development; that's just because that's my background. Having schema evolution and validation wasn't important to me, but those are features that are important to a lot of other people. In the interest of getting more people interested in trying it out I've slowly added those features and I think that rkyv has been made better for it. It's the only of the three ZCD libraries that doesn't support schema evolution, and I think that's going to cause people to choose not to use it. So I'll probably figure out how to get schema evolution in there eventually.

As an aside, I updated the benchmarks yesterday and addressed some other responses that mentioned that the three libraries all have different behavior around validation. That's another place where the three libraries all differ in their approaches and it does materially affect the benchmarks. I found out that Cap'n Proto does validate-on-read, which is is a really cool idea that gives it a big edge while accessing complex structured data that rkyv takes a long time to validate. It's got me thinking about how to get the same kind of validation-on-demand functionality!

(Disclosure: I'm the author of rkyv - thanks for Cap'n Proto, it's been a big influence)