Here is where the bargain ends, and here is where Targum Pseudo-Jonathan slips in the detail most English readers miss.
"I implore mercy before Thee! Let not the anger of the Lord, the Lord of all the world, grow strong, and I will speak only this time. Perhaps ten may be found there; and I and they will pray for mercy upon all the land, and Thou wilt forgive them" (Genesis 18:32).
The Hebrew text has Abraham asking about ten. The Aramaic Targum has him volunteering to be the eleventh. He is not standing outside the minyan, pricing their merit. He is joining them. "I and they will pray for mercy."
This changes the entire posture of the bargain. Abraham is not merely a lawyer arguing for acquittal. He is a member of the jury, a co-petitioner, a man prepared to carry his share of the prayer for a city in which his own name does not yet live.
Ten, incidentally, is the number the rabbis later codified as the threshold for communal prayer — the minyan — throughout the Talmud. Below ten, certain sacred texts are not recited, certain blessings are not spoken. At ten, the Shekhinah (Divine Presence) is understood to dwell in the room.
Abraham stops at ten because below ten, there is no community to save. And he offers himself as the quorum-maker.
The takeaway: the highest form of prayer is not praying for others. It is praying with them.