Ignorance of the UK telecoms market
You show your complete ignorance here, as BT aren't getting a competitive advantage, that's the whole point of Openreach being separated into a firewalled company from the rest of BT, and the Undertakings BT agreed on this with Ofcom.
Openreach deals with BT, in an equivalent manner to Talk Talk, Vodafone, Sky etc... and the rest of the telecoms hangers on.
Ofcom have never pulled BT up on this, and it's very very heavily monitored in BT - ask any BT staffer about Mandatory training, and Undertakings, and they'll groan like having to go to the dentist - *everyone& has to do it regardless of whether they are in telecoms or not - from cleaners, through IT services people to probably even Jake Humphry and Clare Balding on BT Sport.
If you did want a company to be split up who are appearing to be gaining a competitive advantage, how about Sky TV content from Sky TV platform - their shenanigans of fragmenting Sky Sports 1 and 2 TV rights into a plethora of different channels, that aren't offered for rebroadcast by competitors is symptomatic of the behavior they accuse BT of, but have never been able to find any evidence of it - Sky Ryder \cup, Sky Champions league, Sky Sports F1 etc......
........... It could be argued Sky have a dominant position in the UK pay TV market place, the measure Ofcom/competition authorities need to intervene, as it is bad for competition - esp sunce Virgin media hocked their share in UKTV to Sky - Living, Bravo, Virgin 1 etc...a few years back.