The GEC size requirement in 690.47(B) does not exist in 250.54 and therefore might be worth keeping.
Good point
It is arguably unsafe in lightning country for anyone to be connecting an auxiliary electrode to a rooftop array with a 14awg GEC.
I don't personally think its in the scope of the NEC to deal with lightning protection.
NFPA 780 has a chapter (12) devoted to roof top solar systems.
To me 690.47(B) sizing the bonding wire smells like lighting protection and unless I am missing something, could potently conflict with NFPA 780.
For example take the following scenario:
A PV system is installed on a building where 250.66 requires a 3/0 GEC,
A lightning protection system is then installed per NFPA 780,
Per 780 table 4.1.1.1.1 the bonding wire from the roof array to the auxiliary electrode is effectively a #6 AWG (26,240 cir. mil flat braided)
690.47(B) would step in and require this to be a 3/0 bonding wire.
But it is not clear to me where 250 disallows that.
Anyone can run a #14 off any other large electrical equipment on a roof to a 250.54 ground rod if it makes them feel better, so why a special rule for solar ?