I don't get what you are pissed about? Neither the section you quoted or the rest of the document says that you can't have an isolated island of backup power. In fact it explicitly defines those modes of operation. It just says that the island must be physically disconnected from the grid when operating as such and that it must continue to have an earth ground, it cannot rely on the earth ground from the disconnected supply.
It's developed a bit since this post. In part it got worse, in part it got better. The short of it.
The unit I planned was out of stock. I accepted, an at my cost, upgrade and got delivery today.
In the interim I kept looking into the regulations regarding terms like "ESS, Grid-tie, islanding, parallel operation". All of them steer you to G98 and G99 regulations. Born from EU, now GB, but supported by my locality with G98/99(NI).
Unfortunately the "upgrade" was to a Victron Multiplus, which according to it's design is inherently grid-tie, parallel operation. The DNO don't state if it's import or export, just that it's a generator in parallel with the grid.
It IS however <3.8kW which classes it as G98. Requiring only that a qualified electrician "report" it's commissioning within 30 days. Unfortunately the hardware in question does require a G98 certificate of compliance... and Victron do not have one and probably won't provide one.
I am left with 3 options.
1. Let the DNO decide.
2. Use it anyway, just make it temporary consumer installation only, no fixed install.
3. Or return it within my 30day money back guarantee for an inverter only equivalent. Is will NOT have the "AC-in <-> AC-out" relay and will not be capable of parallel operation at all. That brings me back to the basic electrical safety and earthing, which I am happy I can work out with my local spark.