The way I see it, when Ireland became independent, the proportional representation was already envisioned and embedded into the new Irish constitution when other countries, at the time, were pussyfooting on doing the same thing, because their elites benefit from the two party system. Fianna Fail tried to rid of the PR with a referendum in the 1950s, but failed by a razon thin margin. Imagine if ridding PR was successful and we'd be like the US and UK in having a shitshow of politics.

That said, many post-colonial countries either struggled or failed with upholding democracy and becoming rich, while Ireland had been relatively smooth in achieving both. The country had been lucky in that regard.