My understanding is their civilian vs combatant ratio is lower than comparable urban conflicts. So it’s hard to respond “softer”.
Population adjusted, 10/7 was 10x+ worse than 9/11. Challenging to expect zero response.
So what else is there?
Is it the better response under international law? Not necessarily, but it would be better PR.
* a large portion of civilians (and thus civilian casualties) in Mariupol actually identify as ethnic Russians, so it seems unlikely Russia targeted them intentionally
* nobody has filed a genocide case against Russia on the basis of the large number of civilian deaths in Mariupol