Why would Marcion have been a notorious, polarizing, and influential figure at all, if all he did was promote scriptures he himself had nothing to do with composing?
IMHO it was all about the magic, which led to fame/notoriety, which led to wealth and women. Simply, Marcion wasn't on his own. He was part of a stream of thought that people were able to tap into, since Christians had a source in heaven whom could be invoked by anyone. Released from Judaism, Christ became "Open Source". Any cosmic origin backstory became possible, and, as long as it involved angels, daemons and secret knowledge that anyone could access (not just the elite), it would appeal to the masses. Docetists, gnostics and proto-orthodox were all part of that, as independent freelance religion entrepreneurs, just as Paul was. Some contemporaries of Marcion:
Cerdo:
Cerdo (Greek: Κέρδων) was a Syrian Gnostic who was deemed a heretic by the Early Church around the time of his teaching, circa 138 AD. Cerdo started out as a follower of Simon Magus, like Basilides and Saturninus, and taught at about the same time as Valentinus and Marcion...
... Cerdo rejected the law and the prophets, and renounced the Creator, teaching that Christ was the son of the higher good deity, and that he came not in the substance of flesh but in appearance only...
Tertullian, in his work against Marcion, mentions Cerdo four times, but each time only as Marcion's predecessor.
Valentinus:
Valentinus (also spelled Valentinius; c. AD 100 – c. 180) was the best known and, for a time, most successful early Christian Gnostic theologian.[1] He founded his school in Rome...
Valentinus had a large following... Clement of Alexandria records that his followers said that Valentinus was a follower of Theudas, and that Theudas in turn was a follower of Paul the Apostle.[12] Valentinus said that Theudas imparted to him the secret wisdom that Paul had taught privately to his inner circle...
... "he applied himself with all his might to exterminate the truth; and finding the clue of a certain old opinion, he marked out a path for himself with the subtlety of a serpent."
Valentinian literature described the primal being, called Bythos, as the beginning of all things. After ages of silence and contemplation, Bythos gave rise to other beings by a process of emanation. The first series of beings, the aeons, were thirty in number, representing fifteen syzygies or pairs sexually complementary. Through the error of Sophia, one of the lowest aeons, and the ignorance of Sakla, the lower world with its subjection to matter is brought into existence.
Simon Magus:
As described by Epiphanius, in the beginning God had his first thought, his Ennoia, which was female, and that thought was to create the angels. The First Thought then descended into the lower regions and created the angels. But the angels rebelled against her out of jealousy and created the world as her prison, imprisoning her in a female body. Thereafter, she was reincarnated many times, each time being shamed. Her many reincarnations included Helen of Troy, among others, and she finally was reincarnated as Helen, a slave and prostitute in the Phoenician city of Tyre. God then descended in the form of Simon Magus, to rescue his Ennoia, and to confer salvation upon men through knowledge of himself.
Basilides
Basilides (Greek: Βασιλείδης) was an early Christian Gnostic religious teacher in Alexandria, Egypt[1] who taught from 117 to 138 AD,[* 1] and claimed to have inherited his teachings from the apostle Saint Matthias.[2][3] He was a pupil of either the Simonian teacher Menander,[4] or a supposed disciple of Peter named Glaucias.[..
His view of creation, according to the orthodox heresiologists, was likely similar to that of Valentinus, whom he rivaled, being based on a "doctrine of emanations" proceeding from an uncreated, ineffable Pleroma. Like his rival, Basilides taught that matter, and the material universe, are evil, and that the God of the Old Testament, who was responsible for creation, is a misguided archon or lesser deity.[11]
Saturninus of Antioch
Saturninus or Satornilus (active 100–120 AD) was an early Gnostic Christian from the 1st century Simonian school...
Saturninus adhered to Menander's doctrines while Basilides developed them in different ways.[1] However, while Menander called himself the messengers of God, Saturninus considered Jesus Christ the only who could receive this title, and therefore might have been the first teacher to introduce Christ in Gnosticism.[3][4] At the same time, he also introduced the notion of the God of Judaism being an evil impostor, the Platonic idea of a descended spark of life,[5] and the idea that there are different classes of men.
Menander
Menander (Greek: Μένανδρος) was a first-century CE Samaritan Gnostic and magician. He belonged to the school of the Simonians, becoming its leader after the death of his master and instructor, Simon Magus...
Menander called his part of the sect Menandrians, holding the belief that the world was made by angels...
Menander held solid to the belief that as head of the church, he was the savior and Power of God.
All of them recognised that there was a Jesus Christ who lived in Judea amongst the Jews, probably sharing many of the same set of actions and sayings though with different ideas about the nature of Jesus' body. Some had their own Gospels. Basilides apparently used a version of the Gospel of John.