You make a good case overall, but it's important to recognize that if in fact Israel oversees the forced starvation of hundreds of thousands of Gazans, in addition to this being a crime against humanity, it would also be genocidal because there is no credible case to be made that it serves any critical military purpose aside from decimating the civilian population. The action itself would be sufficient proof of intent to physically destroy (an arbitrarily large portion of) the group.

Keep in mind also that while Hamas could surrender, Palestinians in Gaza who are not the Hamas leadership cannot act to avert their own destruction, given that at this point they do not possess the power to challenge Hamas.

Now, it doesn't seem to me that forced starvation is in fact what is going to happen on a large scale, though it's a perilously close thing at this point. It's less clear that the Netanyahu government would avoid it left to its own devices, but at least in concert with the international community it seems likely, if not assured, that a widespread famine caused by military blockade will be averted.