Andrew, you said, “The argument does not require an absolutely sinless life, one that is humanly impossible, only the “one act of righteousness.”
You quote Hebrews several times in this post. I don’t think you mentioned Hebrews 4:15 though: “For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin.” ESV
He was tempted in every respect as we are yet he didn’t sin. That doesn’t at all sound to me like only His obedience to death was all that counted or that it wasn’t necessary that he be absolutely sinless. That is what He did and who He was. Is that humanly possible? My only answer to that is a resounding, no.