Is this a tax? Is it materially different from the universe today?
Social security is an investment, you should consider it as such when budgeting for retirement.
The spouse of a young worker can also receive benefits assuming they have children. But, that’s very much a social program effectively independent of how much money the worker had paid into SS though not their income.
Supplemental Security Income (SSI).
The SSI program pays benefits based on financial need and is intended for low income individuals and families.
If SS taxes where not paying for that money then it would need to come from the general fund. Similarly, with SS doubling your income from 50k to 100k doesn’t double they payout at retirement age. Instead, money is being shifted to support the less fortunate. Further, a married couple with one worker get’s a 50% larger payment than if that same worker never married.
In the end social security doesn’t act like a self funded retirement program.
Also, medicare doesn’t have a cap and is also ignores your 401k.