Note that the federal Natural Response Plan of 2004 was justified partly because of the Congressional Act of 1803. This act provided relief for a fire in Portsmouth, New Hampshire.
However, note that the feds had probably bought land in Portsmouth for dock yard purposes (corrections welcome) using their Clause 17 powers. And if such was the case then federal funding for relief was evidently deemed justifiable under that clause.
It remains that states have never delegated to Congress, via the Constitution, the specific power to provide relief or safeguards against natural disasters for any arbitrary location. The problem is that the Congressional Act of 1803 gives the wrong impression, imo, that Congress can provide such relief and safeguards because citizens no longer understand Congress's limited power to tax and spend.
“Congress is not empowered to tax for those purposes which are within the exclusive province of the States.” —Justice John Marshall, Gibbons v. Ogden, 1824.
I think that federal relief would be appropriate in many cases concerning natural disasters on non-federal land, but the Constitution needs to amended to grant Congress the specific power to provide such relief imo.
I agree with your assessment.