The son gets a market wage for his contributions just like any other employee would. There are actually rules about paying above market wages to family
members to circumvent gift tax laws.
If the equity the son inherits is above what non-family employee would receive for comparable contribution to the company then it would be hard to argue that was earned.
It's interesting how liberals sit on their perch in the ivory tower and just assume that the son in this case works like every other employee. You really have no idea what it takes to run a company, do you? How can you say the son wasn't in the developmental or strategic planning to grow the company? There are many small businesses where the son works much harder for the company than the father. Many where the son is actually the defacto owner, just not in name. Then along comes the government to tax the son when the father passes simply because it passed that law.
You folks are shameless. Take from everyone you can, while at the same time never volunteering to give more.