For a long time the CurrrIO statistic has been profoundly unreliable, and that fact was officially acknowledged as of 184.108.40.20698.
However, the Help for 16.0 still contains this exhortation: When hardware resources are a limiting factor...
"Detecting whether I/O bandwidth is a limiting factor To detect whether I/O bandwidth is a limiting factor, check the CurrIO database statistic. If this statistic is not present on the graph, click the Add Statistics button and click CurrIO. Look for the largest sustained number for this statistic. For example, look for a high plateau on the graph; the wider it is, the more significant the impact. If the graph has sustained values equal to, or greater than 3 + the number of physical disks used by database server, it may indicate that the disk system cannot keep up with the level of database server activity."
That raises the question: Has CurrIO been fixed in 16.0, and can it now be trusted?