Not sure what point you're getting at, but you can see vast majority of trains in Ireland (over 90% from eyeballing this page) are on time[1].
[1] https://www.irishrail.ie/en-ie/about-us/train-punctuality-re...
[1] https://www.irishrail.ie/en-ie/about-us/train-punctuality-re...
You may have had a good experience here in Germany as a tourist, but it's simply not reality. Trains are not reliably on time here these days, and it's a huge problem.
I do not doubt the DART is unreliable in Dublin, the buses are just as bad (I moved to Germany from Dublin a little over a year ago). I know it's a bit apples to oranges comparison between Germany and Ireland, but I can assure you, it is bad here in Germany currently!