Ireland lost two thirds of its population during or after the British induced potato famine, either due to starvation or emigration.
That was before it industrialized and was able to experience a population boom.
Joseon/Korea had a population of around 16 million in 1800 that stagnated during the entire century and only rose again in the 20th century.
Around 60% of that would have been in what is now South Korea.
Before that Ireland wasn't super economically well off, compared to Joseon which was relatively affluent until the 18th century and reached the population arable land could support by the mid 1650s.
Ireland got ravaged by Oliver Cromwell, who launched a campaign of genocide and colonization, which didn't happen with Joseon.
Early medieval Ireland literally only had one single "city", which was Dublin, which was more of a Iron age collection of farmsteads surrounded by a rampart or palisade.
Korea already had during antiquity several major cities that numbered over one or two hundred thousand people such as Gyeongju, Gaegyeong, Seoul and Pyeongyang.
Korea did actually industrialize and had a population curve resembling that. It just happened really fast. Aka educate the population for a educated and skilled workforce, create a manufacturing basis for export to bring in capital such as steel and clothing, build up a steel industry to fuel further manufacturing such as ships, import substitution, increase population growth, more workforce, healthier population, longer lifespan, increased consumption, advancement into electronics, construction and more advanced industries etc. while also being highly protectionist.
Ireland became one of the richest countries from one of the poorest, most agricultural ones in Europe quite recently by becoming a tax haven for multinational companies who relocated all their headquarters to the country such as Ryan Air thus creating a well paying service sector.
Meanwhile there is basically no industrial/manufacturing sector.
The famine left its mark and experienced continued emigration and didn't have any population growth until the 1960s.