I used Holyhead - Dun Laoghaire/Dublin as a train-delivered foot passenger regularly, up to ten years ago. It got steadily more difficult to access the train part here on the Big Island. In the 90s, I could get a train from Stafford at 00:02 to catch the 02:40 boat - with no changes. The last time I looked, I would have had to be at the station for 20:30 to catch the same boat - the timetable changed continuously and there could be two, even three, changes. Coming back here, the train would sit for hours at Holyhead - engine running, lights on and all the doors locked, so you couldn't even get on and settle down. The Waiting Room would also be locked - you just had to hang around a station that looked like a set from a war film, until they deigned to let you on the train. I came to the conclusion that it was deliberate sabotage. The attitude that foot passengers met at Holyhead was little short of open contempt.
My rail journey on the Irish side of the water got steadily better, but, on this side, it just got too difficult. Even buying the ticket here was a difficult process, trying to convince people that it really was possible.
There's little point in synchronising transport on one side of the sea, if people are going to meet the UK's randomised attitude to everything when they get here.