So what are your actual and estimated speeds?
The estimated speed for a clean line is 27.4 - 36.6 Mbps with a handback threshold of 25 Mbps.
The best VDSL sync speed I've ever achieved is 22.4 Mbps.
The estimated speed for an impacted line is 15 - 30 Mbps with a handback threshold of 11.4 Mbps. The BT Wholesale speed estimator says there's no bridge tap, so I guess a have a "copper line condition" - and that's not the same thing as a fault.
You've already highlighted things like the non-twisted pair dropwire which ought to be replaced.
Indeed, just that Openreach won't replace it. They install lines, and fix faults. But old and nasty wiring doesn't count as a fault.
The only other aspect is that these frequencies are used by both VDSL2 and ADSL2+, and so the VDSL2 signals tend to operate at reduced power (adjusted so that the VDSL2 signals from the cabinet are the same strength as ADSL2+ signals from the exchange when they reach the cabinet, so it depends on the distance between exchange and cabinet). So this part of the spectrum often has greatly reduced bitloading on VDSL2 anyway.
Ah, OK. The cabinet is ~2.2 km from the exchange, so the VDSL signals might be down quite a way.