That... is not how wars work. Proportional response is not a requirement.

you don't understand the principle of proportionality "jus in bello", which guides this. TLDR: It's not a scoring competition, it's about balance of means and goals.

Human shields are easy to see, if you're remotely literate in military law: if you don't see the non-combatants clearly marked, as you can observe happening in Ukraine, for example, it's a human shield and a war crime. If you see firing rockets from civilian area, it a human shield because the other side cannot respond and makes more mistakes. If you prevent evacuation of civil population, it's a human shield. Etc.