IOPS are not throughput at all... throughput can't even be calculated until you factor in the size of the I/O request.

You can have 1M IOPS at 5MB/sec if your blocks of data are small enough, like 8k... vs 100k IOPS/sec at 1GB/sec throughput with 1MB request sizes...

In this case 100k IOPS are getting you more throughput than your 1M IOPS.