But remember to add the coming of 2 trains an hour to the Cornwall main line, where there are currently gaps (as I recall) of around 80 minutes at some times of day. There's going to be skill required not only for timetabling the services, but also timetabling them so that the load is spread between the trains.
That's true, but also at certain times of the day there already is a, kind of, half hourly service. Up trains in the morning and down trains in the evening, for example.