17.55 Pearse - Dundalk

[Commuter101]

Hi

Can someone please help me understand why a Dart to Malahide runs what seems like a minute before the 17.55 Pearse - Dundalk commuter train? According to the timetable it leaves Pearse 6 minutes before the commuter train, however on any occasion I've gotten the train, the Dart is delayed, which then results in the train being delayed.
The train then stops at stations (Howth Junction, Portmarnock & Malahide) served by the preceding Dart!
I understand it's "rush hour" but would it not make more sense for the commuter train to run before the Dart??

Thanks!