Good point, prefixes are performance boundaries too, per-prefix rate scaling means you can spread load across prefixes to get aggregate throughput well above 3.5k RPS [1].
But that's a different thing than what the post is about. Even teams that use prefixes for performance don't have an S3-native way to ask what a prefix represents, who owns it, whether it's still accessed, and so on. The semantic layer is missing whether you're hashing for throughput or just laying data out the obvious way.
[1] https://docs.aws.amazon.com/AmazonS3/latest/userguide/optimi...