I live in a village. I mentioned rural as, apparently, that makes a difference.
The cabinet is exactly 100 paces (100m?) from my front door and roughly 400 m from the exchange. Line from the cabinet to me is overhead, if that makes a difference.
For Telephone Bob's benefit it is only three and a half houses away. I over estimated.
I did wonder if the line was aluminium as my parents had a problem with that. The engineer did mention that he'd checked the lin outside and is black not grey so not a problem. I assumed he meant the line from the pole to the house.
Your contract is with BT and not Openreach so it is irrelevant what Openreach say or do as regards who you hold accountable and BT can not shift blame onto Openreach.
It matters not a jot to you that BT have to "sub-contract" to Openreach to provide the infrastructure etc. As said, your contract is with BT.
If BT gave you a minimum guaranteed speed then that is what they have to deliver and if they can not deliver that they are in breach of their contract and guarantee and must either have the problem fixed or allow you leave your contract without any penalty.
See link re guaranteed connection speeds.
When I told the engineer what the minimum guaranteed speed was, he just said "Well you won't get that around here".
The daft thing is that if I'd been quoted a realistically attainable speed in the first place, rather than something that appears impossible, I would probably have been happy.