We didn't know that for GP3 disks, you can increase not only IOPS but also Read/Write Throughput [1] which by default is 125 MB/s. So by default we were not seeing the performance we expected.
Once we increased the throughput of the EBS, it was amazing. So if you are not seeing the performance you read about online when using DuckDB, it may be something like that.
[1] https://docs.aws.amazon.com/emr/latest/ManagementGuide/emr-p...
Is Amazon running on super outdated legacy networking?