The point of war is to achieve the objective of war. It might be to wipe out a certain group of people, but more commonly it is to reduce the enemy’s military, bring about a political reform, and achieve lasting peace.
The just war principles are several. First, the objective of the war must be legitimate compared to the fault of the party against which the war is waged. Genocide, for example, is not considered a legitimate war objective regardless of the gravity of offense. There are other principles I never got to mention on the thread, such as the likelihood of success and unavailability of peaceful means of acheiving a satisfiactory outcome.
Secondly, once the objective of the war is found to be just, its methods are to be just also. Two more principles come into play: discrimination between combatants and non-combatants, and proportionality. Proprotionality does not mean that one should not fight to win; in fact, if the cause of the war is just, one must fight to win. Proportionality means that the military force applied should be sufficient but not exceed the amount of suffering needed to reach the objective. For example, if the objective is to plug supply routes, blowing up apartment blocks and killing as many people as possible has nothing to do with it, but a regime change is likely necessary.
What you seem to fail to understand is that Hamas is dedicated to the goal of eliminating Israel — wiping the country off the planet — making this an existential crisis for Israel, not something to fit into your narrow and weird definition of “just war.”
What you want sounds more like a soccer match played among second graders, where fairness is emphasized over winning.
You talk about theory, yet ignore the facts in hand. The civilians in the buildings are supporting Hamas. If they weren’t, they wouldn’t be there or they would be fighting to overcome Hamas.
The mothers and fathers attempting to protect their children do not see anything “just” in waiting for the next missile or sending their young men and women in on the ground before the missile sources are destroyed.