What could I read to inform myself better on this topic? It is true I had not seen this angle before

This looks pretty informative. The terminology can be hard to follow. https://medium.com/@bounouh.fedi/understanding-iops-in-aws-w...

I/O is hard to benchmark so it's often ignored since you can just scale up your disks. It's a common gotcha in the cloud. It's not a show stopper, but it blows up the savings you might be expecting.