[CydeWeys]

Per the linked article, the London civilian populace was widely equipped with gas masks. A chemical weapon would thus cause fewer fatalities than you might expect.

A 1,000 lb bomb falling on an apartment building, however, would definitely have a significant death toll.

Keep in mind that the total civilian casualty count on the British side during the Battle of Britain was 43k dead and 139k wounded, all from conventional explosives. Those are substantial figures. It's not clear how chemical weapons could have ever remotely killed as many, because after the first few successful attacks the gas masks would be emphasized even more, and everyone would be carrying theirs with them everywhere they went, ready to don at a moment's notice. As the article points out, you can armor even a civilian populace against chemical weapons relatively easily, but you can't armor a city against high explosives.