The writers of the Constitution were not unanimous in their beliefs - the Constitution was a compromise of principles, not a statement of absolute consensus. You're simply declaring the authors whose opinions you agree with to be correct.
James Madison himself opposed versions of the tenth Amendment limiting the Federal government to only the expressly enumerated powers, quoting from Wikipedia here: "James Madison opposed the amendments, stating that "it was impossible to confine a Government to the exercise of express powers; there must necessarily be admitted powers by implication, unless the Constitution descended to recount every minutia."[0]
>It's the federal government that cannot do so -- or at least cannot under the obvious and intended reading of the constitution.
Yes, the Federal government can do so through Congress. The only powers the Federal government is forbidden from exercising are those not enumerated in the Constitution and any others forbidden by the states. Nowhere in the Constitution are the states prohibited from granting powers to the Federal government - which you yourself conceded earlier. Indeed, it would contradict the Tenth Amendment and other parts of the Constitution[1] to claim that states don't have that authority.
[0]https://en.wikipedia.org/wiki/Tenth_Amendment_to_the_United_...
No, in fact it matters very much when the question is what the writers of the Constitution meant and intended.
> The states can literally, and perfectly legally, vote to grant the government additional powers as they deem necessary, without holding a Constitutional congress and ratifying new amendments each time.
Sure, the States can vote themselves social welfare, or anything else that the Constitution doesn't prohibit. You could have California Social Security with no constitutional issues at all. That is clear. It's the federal government that cannot do so -- or at least cannot under the obvious and intended reading of the constitution.