Don't forget the processing effort
Don't forget in these calculations that the CPU doesn't spend 100% of its time reading and writing data from external storage. In fact, with a decent amount of DRAM and clever data mapping, the processor might not read/write that often, depending on the application.
Also, we have to bear in mind that when the processor does 'do work", it may be at the request of an external call (e.g. a website) or some other user interaction that takes time over the network.
All this means the delay from storage I/O might not be that impactful, if we have enough other work to do. Hurrah for large memory caches, multi-tasking and parallel programming!!