It's hard to tell with counterfactuals like that. One factor to bear in mind is that BT was close to rolling out nationwide fibre in the early 90's [0]. Would it have made more sense to decouple infrastructure and service, or would that have led to a nightmare like we have with the trains?

[0] https://www.techradar.com/news/world-of-tech/how-the-uk-lost...