Storage counters at the cluster level

vCenter does not provide information for storage at the cluster level but vRealize Operations does, including counters such as IOPS, Throughput, and Latency. The main reason why you should not look at storage at the cluster level when working with classic arrays is that the cluster is a compute cluster; it is not a storage cluster, so the boundary a cluster provides for compute may not apply to storage.

Can you think of another reason?

The data at this level, like for the ESXi host level, includes all the local datastores. This can impact the overall result, especially those that give an average of all the datastores. If you have a cluster with 10 nodes that share five datastores, you will have 15 datastores in the clusters. The 10 local datastores will skew the total result, masking important data such as average latency.

For a view beyond disk and datastore, the datastore cluster is what you should look into.