You're quite right here, with two exceptions: 1) Fibre transmits photons, not electrons. 2) The fundamental infrastructure limits aren't the cable themselves,

You're quite right here, with two exceptions: 1) Fibre transmits photons, not electrons. 2) The fundamental infrastructure limits aren't the cable themselves, but the equipment at either end. This technology improves every year, permitting the same cables to transfer more data. This is why installing fibre through the streets is such a good investment: it scales up over time, without having to dig it up and replace it. Also, the issue you touched on with customers sharing the same bandwidth is called "contention", and it's possible to determine the "contention ratio" (i.e. how many people are sharing a unit of bandwidth) for ISPs (at least, it is in the UK). Last I checked, in the UK, the contention was always better on DSL services than cable; but the maximum bandwidth and minimum latency on cable is correspondingly better. Though I've not checked the Openreach FTTC offering, which I imagine has a better contention at the moment due to a smaller customer base.