Example for the National Rail Timetable:
Adderley Park: Hourly service, with some trains every 2 hours? (I suppose they could bus it into Birmingham and use New Street?)
Services are no faster than they were under operation of 321 units on the Coventry line, yes there newer. Birmingham International & Coventry have better services, but this mainly down to Arriva Trains Wales. The London Midland service is very irregular, varying between every 25 mins to hourly depending on the stations not everyone wants to go to Birmingham or London. The point I am making for some it has got so much worse.
Adderly Park is not a good example. It is so near the city centre, it is probably quicker and cheaper to take a bus!
Before the timetable change, it was hourly. You say it is now sometimes 2 hourly. From Wikipedia, the station was due to close, but was reprieved. As well from Wikipedia, passenger numbers declined between 2005 and 2007 WHEN THERE WAS NO SERVICE CUT. So it is obvious that people are not seeing this station as important. So a slight service cut is ok.
And I doubt there is a lot of local traffic between small stations. Suburban / commuter lines take people to and from the cities / airport, traffic flows which the new timetable does well.