I realize you are aware of that for your particular installation. What I'm saying is the Code is written from the perspective of not knowing. What if the main bonding jumper at the service disconnect, sized to its tap conductors, is smaller than your [so-called] EGC?
Note there is no such thing as an EGC on the service side of the service disconnecting means.
Let's put it this way... regardless of whether the PV System disconnect is a service disconnect, it is by definition service equipment. 705.12(A) supports this because it refers back to 230.82(6). Note the title of 230.86 is "
Equipment Connected to the Supply Side of Service Disconnect." That makes it service equipment.
Now jump over to 250.80... and while you're there also read 250.92(A) & (B).
Ultimately you have to at the very least connect the enclosure to 1) the grounded [neutral] service conductor, or 2) run a bonding jumper. Either way, the minimum size is per 250.66. So take your pick.
Where I have doubts is when the grounding conductor for the PV side is a combo EGC/GEC. If it's serving the purpose of a GEC, I believe the intent is to have it actually end up going to a GE by way of a GEC, and not by way of the service grounded conductor or a bonding jumper, right? So how does one manage that? Seems to me a GEC has to be run to the disconnect... but the Code does not specifically say you have to. The building GEC(s) can be connected anywhere to the grounded [neutral] service entrance conductor... and it may be sized for the SE taps going to the [normal] service disconnecting means....!!!