... and the idea that a very complex, high performance, multi-seat helicopter can be built under the E/AB rules just seems farcical.
This is one of the core issues. Stuck-wing amateur builders are fiercely protective of their rights and "successes" to date.
Because an old guy in a shed can successfully cobble together a piper cub clone, then this can clearly be extrapolated without concerns to a highly complex type for which there is no successful track record to date.
By questioning the efficacy of the regs that encompass every man in his shed, you are challenging the very fibre of their being and all those who came before, back to the Wright brothers.
When it comes to regulation of all varieties, the US is not the poster child for success, so hopefully the UK regulator will be more thorough, and if loopholes or a lack of clear regulation exist, they close those doors. History tends to show they figure this all out long after the horse has bolted.