Reno:
IMHO, your statement above (#6) is compliant, but....
As the rods are the only "available" 'electrode' I would consider sizing the GEC per table 250.66 based on the OCP of the main. Again I stress this is my opinion.
Yes, I have seen & installed quite a few engineered grounding systems, some which you will say are ridiculous, but...that was the spec.
If this was a new job with footings, then the UFER would have been mandatory, enforced by the Building Inspectors here, using the rebar in the footings, or #4. I guess Tesla likes to 'dig'!
Ideally, when the 'customer' decided to upgrade the parking lot, that would have been a nice time to call OB!
