" I include BT in all this, because they're two halves of the same coin and differentiating them simply allows them to blame each other, obfuscate and put insurmountable obstacles in the way of their customers. "
Ofcom needs to fuck off to doing its homework (technical regulatory matters) and let the Competition and Markets Authority regulate the actual market dominance and monopoly side of things.
Incidentally this is what happened in New Zealand - the NZ version of Ofcom was hopelessly corrupted, claiming there was no problem and happy to accept Telecom NZ's version of Openreach/BT - for exactly the same reason as we see here - Ofcom execs go to/from cushy telco jobs and as such have a very personal conflict of interest preventing them from both acknowledging the extent of the problem or taking action to deal with it.
It was the NZ Ministry of Commerce and Competition Commission that stepped in and forced a separation after noting the amount of damage that had been done to the country's economy by the incumbent telco's anticompetitive behaviour and use of control of access to the last mile network lines as a commercial weapon, along with creative accounting to justify high pricing whilst making it look like the network was a lossmaker (hint: It turned out to be wildly profitable once separated)
BT won't let go of the outside plant because it's both a cash cow AND the best means possible to destroy the competition. No matter what smoke and mirrors are going on, unless the cpmpanies are entirely separated, Openreach is going to remain a glove puppet with BT's controlling fist firmly shoved up its arse.