Re: "between 2007 and December 2014"
"... but many clients refuse to do that because they would also have to provide the benefits of being an employee."
I doubt there is an company that would balk at covering benefits if someone was working for them for a number of years. As long as the rate was reduced to the equivalent of an employee level to be fair.
It would be the contractor who would complain about the drop in rate and the need to pay full taxes.
It's hardly as though someone who has been working at a company for 7 years hasn't taken a holiday or probably even had some sickness. It just they would have to get their employer to pay for it rather than the company they are contracting to and that would be covered by the fees they charge.