That might be true but they still attract capital gains tax and corporation tax.
Then there's all the other expenses of running a business such as accountancy fees, public liability and on going indemnity insurance premiums and business banking fees that an employee won't have to pay on their salary.
What dividends escape is Employers NI and that's where contractors make a gain
Coupled with the ability to have a spouse as a director or shareholder and so income split with them