Let's say that the 20% rate applies to income tax, corporation tax, dividend tax and capital gain tax.
When a company allocates $100 to its employee, the employee receives $100 of salary, pays $20 of income tax, and ends up with $80.
When a company allocates $100 to its shareholder, it's first considered as profit, so the company pays $20 in corporation tax, the shareholder receives $80 of dividends, pays $16 of dividend tax, and ends up with $66.
When a company has $100 profit but does not distribute any dividends, it has to pays $20 in corporation tax, so the shareholder value increases by $80, so if the shareholder sells the share, he receives $80 of capital gain, pays $16 of dividend tax, and ends up with $66.
So, yes, if the all the tax rates are the same, you actually end up taxing capital more than salaried income, which would be a big incentive against creating your own company.