How exactly could M&A regulations be written to prohibit purchasing a potential competitor before it becomes a significant actual competitor? Like what legally enforceable language could you actually use? At some level every business has the potential to become a competitor of every other business.
2. I don't think it's self-evident that regulation would disadvantage US and EU companies. Regulation that encourages competition and innovation is an economic advantage - not a disadvantage. Tiktok might be less attractive if there was a vibrant marketplace of federated social media services that don't send your data to the CCP.