Yes, any zero-copy format in general will have this advantage because reading a value is essentially just a pointer dereference. Most of the message data can be completely ignored, so the CPU never needs to see it. Only the actual data accessed counts towards the limit.

Btw: in my project README I have benchmarks against Cap'N Proto & Google Flatbuffers.

Have you benchmarked against Rust's rkyv, too?

No, I have not benchmarked yet against other languages. Rkyv is Rust only.

One primary difference is that Rkyv does not support in-place mutation. So any modification of a message requires full reserialization, unlike Lite³.

Rkyv supports a limited amount of in-place mutation. But not in general like your approach does.