In an election year, logic has very little to do with it. 10 minute DART frequency looks good on an election leaflet and neither politicians nor media are good with details like average end-to-end journey times. You also didn't mention the cost of frustrated truck drivers hitting barriers which will become at least a weekly event if the barriers spend 3 minutes of every 5 down.
At least this timetable change has prompted me to make serious efforts to serious reduce or entirely end my 4 day a week long-distance commute. After 12 years, I can't take another 20 minutes being added to my day. I'm hopeful I can say goodbye to my pass at renewal time in August.