Well, they are not sustainable, but Ireland no longer relies on them, so it's a moot point. The policies enabled the rapid development over a 25 year period and as the country became richer and the progress became self-sustaining, the arrangements were discontinued.

For example, the "Double Irish" arrangement, which is the subject of this case, was only in use up to 2014 (and was modelled on and often paired with the "Dutch Sandwich" BEPS arrangement, so you should note that Ireland wasn't the only EU country playing these games). It was this case that closed the Double Irish arrangement and while "Green Jersey"/CAIA partially took it's place, the legitimate tax take was already more than sustainable.

Now that Ireland has agreed to a global minimum corporate tax (CT) rate, it's likely that the CT take in Ireland will fall over time, but the inflated CT take of recent years has been treated as a windfall and not current income.