Ireland’s outsize role as the main enforcer of EU data law is divisive. Privacy investigations into social media giants Facebook and TikTok have sparked bitter disputes with regulators in Germany and beyond, prompting repeated claims that the Dublin authorities are ineffective, which they are quick to deny. At issue is the General Data Protection Regulation (GDPR), a labyrinthine body of EU law that was supposed to put manners on Big Tech. For critics seeking sharper and swifter enforcement, the regime is failing. But Europe’s chief data regulator rejects that argument, insisting real progress is being made in the drive to...