Since the blockade only prevented necessities from getting to the civilians in Gaza, but not weapons, then the blockade can only be described as a deliberate attack on civilians, rather than a defensive measure, which is a war crime. It is a war crime to target civilians.

Had the Israeli government honored its part of the ceasefire agreement, whether or not weapons were brought into Gaza would have been irrelevant, since Hamas would not have ended the ceasefire and the weapons would not have been used. So bringing weapons into Gaza has nothing whatever to do with whether or not Israel honored its part of the agreement.