I did not say that NT Wright is making Christological errors per se
Then he's not a heretic because he's within the bounds of the creeds. He may be inconsistent and heterodox, but he's not a heretic. The gospel is not the doctrine of faith alone, but the doctrine of Jesus, the God-man, crucified for sin and resurrected and now either to be accepted or rejected.
That said, unless justification is by grace alone through faith alone, the crucifixion and resurrection of Christ has no point except moral influence, which will (if followed consistently) lead to the denial of those doctrines as well as doubt about the person of Christ (indeed, this was Anselm's reasoning in
Cur Deus Homo) so you're half-right that if Wright, RCs, etc were to follow their own reasoning consistently, they would end up as full-blown heretics. Thankfully, we believe in a God who is able to save us even from consistency.
Do you not believe that justification is the doctrine is essential to the Christian faith
No, I would say that the doctrine of Christ as the God-man who died and was raised. Further, I would say that the doctrine of atonement is far more fundamental than that of
sola fide, indeed justification by faith alone would be meaningless without those I have mentioned. Indeed, Paul talks far more about the atonement and the incarnation than he does about justification by faith alone. That's not to downplay the importance of the doctrine, just to point out that
sola fide is the logical outworking of these two doctrines, and is therefore less fundamental. Indeed, I have known some (mostly RCs) who, while outwardly denying the doctrine, actually practiced it.
Indeed, the RCC and others like them may well be harlot churches, but let us also remember that those are exactly the sorts of people that God loves to return to himself. If I think for a moment that I have all my theological ducks in order and that that somehow makes me all right, how am I any better than the pharisees? The pharisees loved good, proper,
orthodox doctrine. When I read the stories of Jesus and the pharisees, I realize that I'm the pharisee. I need to go down on my knees and repent, saying, "Lord, NT Wright doesn't have it right, but then again neither do I. Thank you for redeeming me in spite of all the ways in which I have misinterpreted your word." Remember that what the doctrine of faith alone means is that no one was ever saved by believing
sola fide: you are saved by believing in Christ. If, in your analysis of NTW, you aren't constantly pointing back to the cross and the fact that Jesus, who was God and man, died to save sinners.
And this is precisely where NTW goes wrong: he fails to apply his own very good theology regarding the death and resurrection of Christ the God-man to the subject of justification. It's no lack of orthodoxy, but a lack of orthodoxy consistently applied, an accusation that condemns all of us, Catholic and Protestant alike.
Thankfully we serve a savior who died to save us from our own lack of consistent orthodoxy.