No law is going to prevent billionaires overnight. At the stage we're in, any political change needs to aim for decades in the future.
Let’s assume a founder has 10%. There are two options to prevent them from becoming a billionaire. Either that company cannot grow past a 10 billion market cap. That would destroy retirement for most normal Americans. The other option is to force the founder to liquidate to pay taxes. If so, then yes, they would stop further building out these companies at a certain market cap once they have no real stake or say in them anymore. Why would they work for free once they are at the limit. I wouldn’t and I think almost nobody would.
Billionaires are a symptom of a problem that the US had under control for almost half a century until Reagan basically broke American economic policy.