Fred,

What did John repent of if it wasn't heresy? He tampered with the second person of the Trinity in a way that was outside orthodoxy did he not? If the Second Person of the Trinity was not the eternal Son but became the Son, then the doctrine of the ontological Trinity would be tampered with beyond the bounds of orthodoxy. The Son's relationship to the Father in the covenant of redemption would too be in shambles. A quick test for heresy is that if the doctrine were true, Christianity would be false. Well, if the Son were not eternal in his relationship to the Father, then Christianity is lost. John misunderstood the eternal unity of the Godhead yet wanted to maintain the particulars; but the Trinity is unity and diversity, which a denial of the eternal Sonship undermines. There's a lot more to Trinitarian theology than affirming three persons. The eternal Sonship is just one example of orthodoxy.

Ron