No, YOU look again at the Gregorian Missal. The Secret WAS the Offertory. It was said silently up until about the fourteenth century. The earliest versions did exactly what later Offertory prayers do--ask God to receive the sacrifice we offer, etc. I've also taken note of the Dominican rite--and there is indeed an Offertory, strikingly different from what you find in the Novus Ordo--which is a mere prayer of thanksgiving before a meal and which focuses on the benefits to US of what will become the "bread of life" and "our spiritual drink"--and which nowhere mentions the Propitiatory Sacrifice of the Son to the Father in expiation for our sins. The whole concept of sacrifice is radically different in the Novus Ordo, with the vicarious satisfaction of Christ implicitly rejected.
No, it isn't. Sacrifice is explicitly mentioned.
P: Orate, fratres: ut meum ac vestrum sacrificium acceptabile fiat apud Deum Patrem omnipotem.S: Suscipiat Dominus sacrificium de manibus tuis ad laudem et gloriam nominis sui, ad utilitatem quoque nostram totius que Ecclesiae suae sanctae.
"sacrificium de manibus tuis" is a clear reference to the Eucharistic sacrifice of Christ, as opposed to the "vestrum" sacrifice of praise and thanksgiving.
P: In spiritu humilitatis et in animo contrito suscipiamur a te, Domine; et sic fiat sacrificium nostrum in conspectu tuo hodie, ut placeat tibi, Domine Deus.
The Novus Ordo has mostly the same Secrets as the Gregorian Missal and Tridentine Missal. Some are from other ancient Missals. See here, which includes, sources and accurate translations:
http://www.geocities.com/Athens/Parthenon/8881/liturgy/prayers/prayers.html
If the propitiary nature was sufficiently demonstrated by the Secret in the Gregorian Missal, than the same is certainly good enough for the Novus Ordo too.