I'm a contractor myself and made up rates are still a thing. The high end isn't any better than jobs I can see advertising for perms, and many of the companies advertise for perms before they'll consider contracts.
There's actually 3 companies that have been looking for my skillset for around the last 3 months, and they all refuse to even have a call with me because I don't fit in the rate bracket, but they'll keep looking regardless.
Maybe earning double is an exaggeration on my part though. For myself I earn 50% more as a contractor than as permanent (this is the net amount after taxes, holidays, accountant fees etc.)
Contractor: (Devops, high day rate)
750 x 220 = £165,000. 800 x 220 = £176,000.
Employee: (Devops, high salary) + Employers NI.
150,000 + 19,508.78 = £169,508.78
Said contractor would need to bring his own equipment, pay insurance, and deal with the risk of being let go arbitrarily, and won't get a bonus or pension contribs.
Now where the contractor can make out is, he can pay reasonable expenses, and he can act more tax efficent, especially if he doesn't pay himself more than the higher threshold.
For the record, I'm not a big fan of the politics that comes with being an employee, I like to just come in, do the work, and leave, so quite happy as a contractor.
These usually don't reflect that skilled IT is vastly different from desktop jocky, and that it's a well paid field, thus they're forced to use contractors or outsource.
Skill wise, they're probably same same.