The point is that EU regulations may prevent the creation of monopolies in the first place, so EU countries are unlikely to be a source of alternative monopolie

The point is that EU regulations may prevent the creation of monopolies in the first place, so EU countries are unlikely to be a source of alternative monopolies to the existing US ones. So there's cause to think it unlikely that we'd be trading a "devil we know" that is at least partly accountable to US institutions, for a "devil we don't" that is less/not accountable.