No, it's a pseudo-Ponzi scheme.
The government does not claim, nor does it promise, that your FICA taxes belong to you. If they did, it would be a Ponzi scheme.
If you want to BELIEVE that your "contributions" belong to you, that's fine with the Feds. But their actual position, both as to law and as to fact, is not difficult to discover.
Remember people sued Carter when he raised the retirement age in the 1970’s. Plaintiff argued that the gov had a contract with the people. Another myth. SCOTUS ruled SS is a legislated entitlement and Congress is granted wide latitude to change it. In other words, Congress can spend all of SS money on a one month sex orgy on the Wash DC mall and the only thing the American people can do is vote the bastards out of office. That is why SS is the worst “contract” to accept. Atleast a 401k is your money and the provider has contractual obligations to the original terms of the agreement and one can sue them if they violate the contractual terms. SS does not have this feature.