Firstly the EU doesn’t have the same requirements as the Chinese anti trust authorities, secondly it’s not about what they could do in theory but want can do in practice it’s politically impossible for the EU to block it now with Brexit going on.
This isn't about Brexit being a distraction, it's about their mandate and optics.
Until the 31st of December the DG COMP actually needs not only to show that there is a sufficient reason to investigate the deal, but that the CMA ruling wasn't in line with the TFEU.