wonder why we would bother trying to defend something (the illusion that excess domestic production can be sent to share with others
It's not an illusion. There are around 500,000 11KV -> 240V substations in the UK, and around 50 million domestic meters, so an average of 100 homes per substation. Excess solar generation from one home can be used by any or all of the homes downstream of the substation, thus reducing the draw across the substation transformers and consequently the total load on the grid.
It's a few years out of date now, and doesn't specifically address issues of micro solar generation, but this free book is a really good run-down on how the industry, especially the wholesale market, works.
https://www.cgi.com/uk/en-gb/gb-electricity-for-dummies
