Even before, there was no digital single market for services. The previous single market was only for manufactured goods. So that didn't affect startups in UK to be successful. We can expect the same after Brexit.
Right to Privacy is being eroded also in US with the new FTC rulings. So that is not a valid disadvantage.
Considering the recent events, Brexit if it ever happens, will be a Soft Brexit as the UK Govt doesn't anymore have the required mandate or support for a Hard Brexit that wrecks the economy.