The benchmark is specifically done on the encoding/decoding steps on the formats. But Cap'n Proto does not have that, so it is, in effect infinitely faster for this step.
Weird as it sounds, put a mirror in front of another, same size and shape better. The reflection will vound "infinitely" from one mirror to the other creating a "never-ending" effect of mirrors inside other mirrors.
In my university gym changing rooms there were two mirrors in front of each other like that.
First time I saw it it kept me thinking about infinity :D
The benchmark is specifically done on the encoding/decoding steps on the formats. But Cap'n Proto does not have that, so it is, in effect infinitely faster for this step.