The other problem with the "replacement" service is that it doesn't appear on the IE timetable since it's a BE service, so what little feed trickles through onto the rest of the network disappears because it's not convenient for casual browsers to make connections.
That said, I looked at the route in Google Maps and it's one field after another and not even a bullet straight route like Glounthaune-Youghal at that, instead winding along with plenty of LCs and the opening Barrow bridge to be maintained.
Ironically, one of the things IE blame for not being able to run later is that the 1720 ex Waterford is crewed from Waterford, and the bus from Rosslare they get back to base leaves at 1900. If it left 15-20 minutes later, it could pick up trade from the 1933 arrival ex Heuston as well as those still trying to get across the river from where most people work. That would mean the crew would miss their bus... or Bus Eireann could be asked to delay their service by 15 minutes. Nah, that would violate Mary Harney's precious competition between rail and bus.
At the very least IE should be leaned on to redirect that equipment to Carlow for a commuter service - it's a bit ridiculous that there's no arrival from that side into Waterford before 0945.