Sin/Grace versus Law/Gospel

Caveat Emptor! Theology is the topic!
So, I hear a lot of sin/grace preaching these days, and after forty years of it, I'm still not convinced. Sin/Grace preaching basically says that we sin, (usually in observable ways by others), but God's grace "saves" us in one way or another. This is certainly one way to read the Bible but it is only ONE way, and to my mind not the best way at all. This way of understanding the Christian life seems to make too big a deal of human capacity to appease, please, assuage, or manipulate God for me. At some level the "sin" has to be turned over, acknowledged, repented of in order for God's grace to take action, and this seems a little too optimistic of the human condition for me to believe. Basically, if humans have the power to repent, then they have the power not to sin, and since they sin, well, they must not have the power...and that's too negative of the human condition...
I grew up understanding my tradition (and although I always heard it as THE ONE WAY to read scripture and Christian life, I've since learned there are others...) to be about God's law and God's gospel. The law is that of God that cannot be abrogated, annulled, or ignored. But God's promise (to love humanity through the death and resurrection of Jesus Christ) also cannot be denied, and this promise always trumps God's law. This seems to be a more realistic way to read the Divine and Human relationship, as it puts the human capacity to change on the back burner, and instead focuses on the human capacity to live under the promise in the realm of God's law. How might this matter....? Consider this story.
A young woman, age 22, wakes up on Sunday morning to watch a guy get dressed. She can't really remember his last name, but he was poilite, and nice, and sometimes that's enough...As she watches him leave for his softball game, or maybe football, (she really wasn't listening to what he said), she decides to head over to her local Christian congregation for some church. Now, if she gets to a sin/grace type of place, she's going to hear that her choices over the past 24 hourse were not exactly what God had intended for her, in fact, it is her heart as well as her behavior that needs some adjusting, and God's grace will take care of that. (At this point, in the sin/grace story, depending upon whether she landed in a liberal or conservative place, the grace either will be there for the taking, or she will have to repent to get the grace.) She hears one thing that gives her hope, but also depresses her...if there' going to be any change for next Saturday night, that change is up to her. And so it goes...
Now, if she lands in a place where the Christian life is viewed in a law/gospel context, she will hear the same sort of things, but in a different key. God's creation and law are designed for us to flourish and live, and her choices over the past 24 hours did not always align with that design. However, those choices cannot erase the promise of God she has received, so the promise continues to exert pressure on her to live as a child of God. What she hears here is that change or not, God's promise is still for her, and how her life lives out comes from God's urging for us to flourish. Will she change by next Saturday? And so it goes...
The sin/grace dichotomy of Christianity has a long and distinguished history, and it would take many more words to do justice to beauty of the tradition in someone like Aquinas or Calvin. I'm not writing to say that Law/Gospel is right, and all others are wrong...those debates don't interest me much...But I am writing to say that sin/grace on one hand seems too easy (just turn to God), and on the other hand too hard (don't make God angry); whereas Law/Gospel just seems too hard...Live, as if the promise of God's love for you will never die..