So aside from all issues of code and legality, im trying to figure out which purposes we are attempting to serve with this ground conductor..
If lightning strikes your array and the lowest resistance path to ground is across your MPPT, *bad stuff*. So a grounding rod at the array OR a conductor back to 'house' ground would protect against equipment damage there, i guess. Ground rod would probably be a bit better due to the extra ~200' of wire in the other option.
If your inverter is putting AC voltage your PV circuit (which is apparently common?), and you were to come in contact with it because you had unplugged the PV and assumed the house-side line was dead without checking, etc.. then whether you get the privilege of experiencing that AC voltage basically comes down to what else you're touching and whether it presents a low enough resistance 'path back to source'. In that scenario having a local ground rod would make the ground you're standing on (assuming ground mount because we're talking about driving ground rods) and basically everything sitting on the ground, a better path back to source than if there were no ground rod there at all... so not helping.
But, if you had a dedicated ground conductor then ONLY the PV framework, mounting rails, and that actual conductor would be a 'good' path back to source and the rest of the ground you're standing on would be a pretty poor one considering the 150'. Unless your ground mount is on metal posts driven into the ground in which case, not much better because unless you took steps to electrically isolate the panels from their mounting system then the local dirt itself would have a good path back into your dedicated grounding conductor through the mount!
So the dedicated ground conductor is preferable (again, regardless of laws/code) because while it does a slightly worse job of protecting from lightning, it does a better job of protecting you from AC faults that may exist on your ostensibly DC circuit if you also happen to not be wearing shoes?! What am I missing here? I feel like there must be a better reason than that.