Comment by jjav
> which would all be salary going to you
That part is not necessarily (or even probably) true, if payroll tax didn't exist the company might not pay all of that to you unless they had to.
But that's a nitpick... overall, it is true that the fully burdened cost of having that employee is X+Y, so that's the number the company needs to consider when deciding whether they can afford to hire (or keep) this person or not.
The competitive market would take care of that. The employer that most wants your services will offer the X+Y, and competition will induce others to do the same. (No, the job market isn't perfectly liquid, but in principle that's what would happen.)