Obviously, God’s calling Eve ‘ezer does not mean that Eve is subordinate to Adam or that women are subordinate to men.
Perhaps our difficulty in interpreting ‘ezer can be better seen by noticing how we use “helper” in English. We speak of “mother’s little helper,” a “plumber’s helper,” being a “good helper.” In current English, “helper” carries the connotation of a subordinate — even a child.
Thus, if I were drowning, I’d call out, “Help!” But I wouldn’t refer to the person who rescued me as my “helper.” My rescuer truly helped me, but calling him “helper” would be too condescending — even belittling.
But these thoughts are utterly foreign to the Hebrew ‘ezer. There is no condescension in the Hebrew word at all, so that “helper” (or “help meet,” as in the King James Version) is truly a clumsy translation. In other verses, ‘ezer is used in the sense of “rescuer” or “liberator.” The word is also used in the sense of “one who fights alongside against a common foe.” “Comrade” or “ally” would come close to the sense in many contexts. Thus, the psalmist sings that God is Israel’s help, not a mere helper — but an ally so powerful that Israel must prevail.
When the United States’ armed forces came to the rescue of Kuwait, we were there to help, but we were not helpers — the U.S. military was an ally, a comrade, and an overwhelming superior to any military capability that Kuwait could have mustered. This is the sense ‘ezer used with respect to God and His relationship to His people.
“Complement” is therefore a proper if not excellent translation.