That doesnt mean regimes we respect should retroactively apply new rules in unpredictable ways
They just found that Ireland's tax rules from 1991 and 2007 are illegal tax benefits according to the preexisting rule.
Just because they took so long apply existing law doesn't make it retroactive.
This is a retroactive ruling. This is playing favorites, the opposite game.
Same with the data contracts with the US, Safe Harbor, Privacy Shield etc. All approved, all later on found a violation of EU law.
That's not retroactive just slow.
The central difference of opinion is of course whether outright gaming the system is acceptable regardless of the written rules being followed to the letter.