NEC is not a source for design criteria but a BARE MINIMUM standard to ensure safety to life. But if followed by 25 ohms maximum resitance rule satisfied by a single ground rod in a large outdoor substation, it could lead to electrocution on HV ground fault.
Any substation owned by the POCO is not covered by the NEC. Only those owned by private companies are, and they will be rather small.
Regardless, every substation I have ever seen does not rely on ground rods for earthing. Again, the 25 ohms is a bare minimum for a single rod. At a residence in my area, two rods only get around 200 - 500 ohms. A single rod, in a test, measured 1300 ohms. We have sandy soil here. So, most residences only have 200 - 500 ohms resistance. If more were needed to reduce a hazard it would be stated as such.
The grounding at a sub station is more focused on lighting protection than line to ground faults. As such, they are overkill for the utility voltage and current capacity just by design. I have seen electrode conductors in the 750 MCM range on sub stations. Those sure aren't going to a ground rod.
TAKE maintenance into account
1) What kind of maintenance is there for ground rods?
2) How is maintenance going to eliminate the changes due to weather? Any ground rod will have a varying resistance due to the moisture content of the soil, which usually goes from dry to wet during the course of the year.
If an electrolytic ground is used, there is maintenance that can be done to insure stability.