You don't need to mess with prefixing all your files. They auto level the cluster for you [1].
[1] https://cloud.google.com/storage/docs/request-rate#redistrib...
https://aws.amazon.com/about-aws/whats-new/2018/07/amazon-s3...
https://aws.amazon.com/about-aws/whats-new/2018/07/amazon-s3...