Startups, or the companies that they would later turn into would have a substantial tax burden keeping them down. (You can't hide an economic inefficiency - the effect of taxing to pay for it would have a negative impact.)
The "economic inefficiency" associated with a guaranteed minimum income, or wage subsidy, plus a basic level of government provided health insurance, has less distortionary consequences than the current system with a minimum wage and employer-provided insurance.
But really, this kind of reduction in inequality has generally quite positive effects on economic growth and productivity, and everyone in the society, including the rich, winds up better off after the improvements have compounded for a few decades.
There is no such thing as a free lunch.