Bandwidth is speed in most cases for the internet, lag intolerant games being an exception. Also my 10Mbit link is good enough for me despite having 100Mbit available. So the question is about comparing things which are not really comparable. Well, TBF, I can't.
> Passengers may value the speed more than the capacity
well they might, and they might want the carriages painted polkadot with hot podium dancers at each end, so how about arguing from a basis of fact instead?
from https://press.which.co.uk/whichpressreleases/rail-companies-... and with a table at the bottom. Speed is not mentioned in the report. Clearly other things really are hurting them.
As to speed vs capacity, look in the chart at 'standing room' and 'availability of seats'. That's about capacity.
> Door to door train v car journey is more marginal that what you suggest
For you I wouldn't doubt, but there's a lot of others who may feel different. Pace but arguing from 1 data point is not rigorous. I've heard of people spending £5,000 a year for their work commute (that may be reporting bias but it's another data point).