By definition of the word RANSOM, it is an exact and equal exchange – one life perfect life (Jesus) for one perfect life (Adam) – NOT one life for many lives.
Following are definitions provided by New Testament Greek Scholars:
Adam Clarke’s Commentary: Verse 6. Who gave himself a ransom The word lutron signifies a ransom paid for the redemption of a captive; and antilutron, the word used here, and applied to the death of Christ, signifies that ransom which consists in the exchange of one person for another, or the redemption of life by life…
Jamieson, Fausset, Brown Commentary: ransom—properly of a captive slave. Man was the captive slave of Satan, sold under sin. He was unable to ransom himself, because absolute obedience is due to God, and therefore no act of ours can satisfy for the least offense. #Le 25:48 allowed one sold captive to be redeemed by one of his brethren. The Son of God, therefore, became man in order that, being made like unto us in all things, sin only excepted, as our elder brother He should redeem us (#Mt 20:28 Eph 1:7 1Pe 1:18,19). The Greek implies not merely ransom, but a substituted or equivalent ransom: the Greek preposition, “anti,” implying reciprocity and vicarious substitution.
Nazarene Commentary 2000: ² A substitionary ransom: The Greek is unique here, ANTI-LYTRON [Strong’s Concordance <487>, corresponding, opposite, atonement, redemptive price].
Matthew Poole’s Commentary: Ver. 6. Antilutron, the word here translated ransom, is very emphatical; it signifies the exchanging of condition with another, the laying down of one’s life to save another’s.
The Pulpit Commentary: What means a ransom? …It is the price given as an equivalent for setting free the prisoner, or sparing the forfeited life;
Robertson’s NT Word Pictures: A ransom for all (antilutron uper pantwn). “A reminiscence of the Lord’s own saying” (Lock) in #Mt 20:28 (#Mr 10:45) where we have lutron anti pollwn. In the papyri uper is the ordinary preposition for the notion of substitution where benefit is involved as in this passage. anti has more the idea of exchange and antilutron uper combines both ideas. lutron is the common word for ransom for a slave or a prisoner.
John Wesley Notes on the Bible: Verse 6. Who gave himself a ransom for all—Such a ransom, the word signifies, wherein a like or equal is given; as an eye for an eye, or life for life: and this ransom,
Parkhurst’s A Greek and English Lexicon of the New Testament (p. 47): a ransom, price of redemption, or rather a correspondent ransom. ‘It properly signifies a price by which captives are redeemed from the enemy; and that kind of exchange in which the life of one is redeemed by the life of another.’ So Aristotle uses the verb antilytroo for redeeming life by life.”