I could not agree with you more. It is among the only "no-lose" prayers that we know of by Christ's examples. Again from the passage:
1 John 5:14-15 : 14 This is the confidence we have in approaching God: that if we ask anything according to his will, he hears us. 15 And if we know that he hears us whatever we ask we know that we have what we asked of him.
In this case, when we make it up, there is a full possibility of "losing". That is, if it is not in accordance with God's will. With the Lord's Prayer, that is not possible. My point was to note that God does actively wish for us to attempt to pray in His will in addition to the Lord's Prayer.
I couldn't have said it better, FK. Thank you. Your definition captures the essential difference between our God-given Prayer, in His own divine words, and our made up prayers.