I think that's where you and the other commentator are talking past each other. Amazon tends to have great managers and senior ICs that get the responsibility and technical divide right.
My experiences outside Amazon unfortunately point towards this being hard to get right in the first instance, and really really hard to fix once it has gone wrong.
You can make quick decisions because you don't have to communicate with a large group. You don't have to communicate with a large group because you own your space. You own your space because you have clear external interfaces.
If the external interface needs to change (from your side or the other side), it requires external communication and is probably slow, so you (and the other side) try to get it right the first time and minimize changes.