Much like China, which has managed to develop a huge internet industry because it doesn't have to compete with the American competitors, the EU's huge market will provide a lot of space for EU startups if the American competitors refuse to do business in Europe. But unlike China, the GDPR will make those European companies more competitive on the world scene rather than less.

If the choice was between 2 services, one of which complied with GDPR and one which didn't, and explicitly excluded GDPR protected users, I'd assume the vast majority of regular consumers, but definitely businesses, would pick the GDPR compliant one.