Metanoia means a change of mind... but the Scriptural context of metanoia helps us understand the object of what we are changing our minds about.
The context of repentance in the NT often involves "repentance for the forgiveness of sins" and "calling sinners to repentance"
So in the NT (and the OT for that matter) repentance does indeed involve a "change of mind" regarding sin.
And as I mention above, that "change of mind" regarding sin involves deciding that I no longer want to be a slave to sin and that I want to be delivered from sin.
So there there is a way to understand the phrase "turning from sin" that is an accurate understanding of the Scriptural principle of a "change of mind" regarding sin.
And based on what "turning from sin" means to you, I agree with what you are saying.If "turning from sin" were a requirement for salvation, we'd all be lost. If one wants to claim that turning from sin is a part or sanctification, then I'd agree.
But the issue here is "turning from sin" means something totally different to claysmith than what it means to you.
So when you and claysmith are discussing whether "turning from sin" is a Scripturally accurate definition of repentance you are just talking past each other.
Based on how metanoia is used throughout the NT I would also add that metamoia also involves changing your mind about sin.But it's not metanoia, and turning from sin is not the part of trusting/faith that saves. "Repent and believe", more accurately is "change your mind (about who Christ is, and what he's done), and believe".
Trusting Jesus to save me from my sin involves.
Turning TO Jesus to deliver me FROM my sin.