Depending on what your routes and usage, higher speed is better than more frequent service.
For example, let's say your options are a 2 hour train that runs hourly, and an hour long ride that departs every other hour.
* Fast train: best case, 1 hour. Worst case, 2:59. Average case - about 2 hours.
* Slow train: best case, 2 hours. Worst case: 2:59. Average case - about 2.5 hours.
Of course this is one example - but there are definitely cases where increased speed is strictly better than increased frequency. (Unless being on the train is better than whatever you could be doing waiting for the train)
The reality though is that high speed trains aren't nearly as fast as you'd think from the claims of 250-300 km/h top speeds. Particularly in Germany, 130kph average speed on a route is very good. Replacing a 100kph train with a 130kph train doesn't make an enormous difference. In order to get double the usual speed, you need to have totally dedicated tracks, end-to-end, and they haven't done that in most places. Having trains run more often makes a huge difference in convenience and also allows you to not worry too much about missing your train.
For example, let's say your options are a 2 hour train that runs hourly, and an hour long ride that departs every other hour.
* Fast train: best case, 1 hour. Worst case, 2:59. Average case - about 2 hours. * Slow train: best case, 2 hours. Worst case: 2:59. Average case - about 2.5 hours.
Of course this is one example - but there are definitely cases where increased speed is strictly better than increased frequency. (Unless being on the train is better than whatever you could be doing waiting for the train)