Currently there are very few configuration options for users to customize how the s3-repository module interacts with S3.
One such option that would be very beneficial, especially given how many files Solr backups can use, would be retry and throttling logic. The AWS client provides a few options to customize the number of retries, and backoff logic, when requests do not succeed.
We don't want to give users a 1000 options to configure the S3 client in the solr.xml, but we can definitely give a few popular options that would help optimize for their use cases. Retries and throttling backoff logic seem like 2 good options to start with.