That assumes cross-tenant compression.

Compression and content-addressing are two separate things.

Content addressing across accounts on private, AWS encrypted S3 buckets would run counter to their claims.

A couple of comments across the thread have made similar points, but if I were implementing this, the "client metadata" like the incoming sha256 etc would be implemented a layer higher than the actual byte storage, so the byte storage could be compressed without any impact on that sort of thing.