O.K. - Openreach is a still BT group company. Perhaps I could/should have distinguished between BT as a whole & Openreach.
What we do
Our 21,000 Openreach field engineers make around 3.2 million visits every year to install, repair and maintain the network that makes communication possible. Openreach is also committed to delivering a broadband capable network that strives to meet future bandwidth demands.
We work on behalf of the 400+ Communications Providers (CPs) in the UK – providing an identical and equivalent service to all.
Although part of the BT Group, Openreach engineers are dedicated to supporting Openreach. As a result they treat other BT lines of business in exactly the same way as they treat all other CPs in the UK.
Each ISP has equal access to both BT Wholesale and Openreach to deal with broadband issues. While one ISP may seem to have better results in getting things sorted, ultimately, regardless of which ISP you are with it'll be the same Openreach engineers who visit.
I think you are referring to the terms of "Equivalence" that BT/Openreach have to adhere to, in that they are not allowed to give preferential treatment to any ISP, even if it is owned by another part of the BT group of companies.
AAISP did build a reputation at one time for getting things fixed.
From what I have read recently, under these "Equivalence" terms they appear to be less successful.
My ISP is actually owned by BT, but they also have to be treated exactly the same as any other ISP.
The point I was trying to make was that it is very easy to blame an ISP for connection problems. However, if the aged infrastructure (wires etc.) is just not up to it, whoever is responsible for maintaining/repairing the infrastructure is at blame.