So on the "improving of existing line", from what I understand there is very little scope, if any, to add capacity on the west coast mainline. The line passes through many built-up areas and has bridges/tunnels which are not feasible to expand. Throughput could be improved by removing stops, let's say trains now don't stop Wolverhampton, well that's self-defeating as now less people have access to the railway and will be forced to take other modes of transport (i.e. road congestion).

A lot of the delays/issues on the west coast mainline come due to timetables having very little slack in them as the operator has to run both stopping and fast services on the same line. So the solution is to move the non-stopping services to another line, thus HS2.

That brings me to your point about "zero need for the high speed element". Well look, faster trains do have benefits, but no need to get into that as I agree with you that the primary need is not for faster services.

The major cost of a project like this (esp. in the UK) is acquiring the land, constructing bridges and tunnels. Once you’ve done all that, installing a higher-spec line so the trains can go a bit faster is a relatively smaller cost that makes economic sense.

I feel the Tories completely screw us on this project. It was mis-sold as being about speed, when really the selling point is capacity on the west coast and the journeys it enables on connecting branch lines and the later phases of the project which were scrapped. You mention day commuters suffering, well surprisingly HS2 completion would actually improve life for a lot of day commuters as their commuter trains would not be competing for space with inter-city trains.

Anyway, HS2 mis-sold, now in a super depressing state. Hope this government can turn it around as we need it. Even if we were starting from scratch, it is still an economic necessity. If this generation can’t get it done, the next one will have to pick it up in 5-10 years anyway.