> If that tax advantage disappears one would expect multinationals to rearrange their affairs

To be clear, the ruling relates to a state of affairs which existed from 1980-2014, and the issue in question was whether Apple was given a special tax deal relative to other companies (which the EU generally doesn't allow outside very limited cases). It has no bearing on Ireland tax rules in 2024.

> and we should see a rapid decrease in Ireland’s GDP over the next few years.

This would arguably in itself be no bad thing; Ireland has one of the highest GDPs per capita in the world, and the highest of any country with a population greater than a million people (the rest are microstates plus Luxembourg). This artificially inflated GDP causes some problems; in particular it increases Ireland's EU contributions above where they'd otherwise be. Ireland pays more per capita to the EU than any other country.