Yes, I've been throttled many times by S3. My largest database is ingesting ~5PB/day and that turns into a lot of files in S3. At one point we changed our S3 key scheme to not have hashes up front, which unlocked some simplicity in control plane operations like deleting old files; we did this on the strength of the announcement from AWS that you no longer needed to get clever with prefixes.

This was incorrect at our scale, and we had to switch back.