I don't see much evidence of the quality getting worse. I remember the state of the bus service in Cork in the 1990s and it was absolutely awful. The city / outer suburban busses used to be cast offs from Dublin Bus, often with all of the green branding inside and a Bus Eireann paint job. A lot of them could barely make it up hills, puffed smoke and were in very poor condition generally.
I also remember Bus Éireann running busses to Cork's satellite towns like Carriagline from Parnell Place bus station and having no indication of which bus went where - they didn't have the correct rollers with Cork destinations (possibly still old Dublin Bus rollers) or they didn't bother using them. I didn't even realise that there was a bus number for any of those routes.
It was like something you'd expect to see in pre-EU Eastern Europe.
The state of some of the trains before the last major fleet upgrade was also very patchy. There were modern 1980s intericites, but you could equally pay for a normal ticket and end up on some 1960s/70s bone shaker or even a commuter DMU on Cork-Dublin if you were unlucky. At least nowadays you can be sure of a modern intercity train with fairly reasonable facilities.
I remember when I was maybe 12/13 going on late night trains from Dublin to Cork that were some kind of old BR intercity design and it often had no heat on a winter's night. You'd be sitting there in a coat with steam coming off your breath, desperately trying warm yourself on a cup of tea!
There was no golden age of CIE or Irish public transport. It was always bad. Or, at the very least it was always very patchy and unpredictable. You could get modernity on one bus / train and then something out of a scrap yard on the next one.