Backhaul from the masts well on the West side of the country at least is on the same IP network as the broadband. Same as Cody I was part of CWW.
4G Masts are usually on 1Gig fibre bearers back to a local IP node, where it connects onto the 10Gig rings. BT Openreach FTTC handoff is at the same location.
What does this mean? It means that a lot of ISP’s utilise BT to backhaul their customer traffic to a number of interconnects to the ISP’s own network, as such they are at the mercy of BT and a finite amount of bandwidth shared across a large number of other ISP’s customer traffic as well as their own. In Vodafone’s case as the handover is at the local exchange direct onto the Vodafone IP network then a lots less customer traffic fighting for space on a large amount of bandwidth.
Yes the investment is the same up to a point, well at least from the mast back to the core. Mobile signal coverage and speed is dependent on a lot of factors other than just the backhaul bandwidth but that IP network is seriously beefy and one thing I don’t ever hear about is any congestion on that core.
I’ve been a user of the same broadband since it came out, router works well enough, never had any issues with variable throughput. But always remember you are still at the mercy of BT Openreach and their local cabling performance.