Did complementarians invent the notion that beings can be equal in essence and yet one be subordinate to the other in terms of function or role? That’s what many egalitarians claim.
Here’s an interesting selection from Ambrosiaster:
The subjection of Christ to the Father means that every creature will learn that he is subject to Christ, who in turn is subject to the Father, and will thus confess that there is only one God. But Christ’s subjection to the Father is not the same thing as our subjection to the Son, because our subjection is one of dependence and not the union of equals.1
“Christ’s subjection to the Father is . . . one of . . . the union of equals.” The notion that a being can be equal in one sense yet subject in another sense is quite apparently not novel.