And despite masking, COVID spread all over the globe and killed a fuckload of people.

Would more people have died if there was no masking? Yes, absolutely.

But the question of interest is: how many fewer people would have died if we made a concentrated effort to improve ventilation in public spaces?

Maybe I'm completely missing your point, or maybe you're just being snarky/contrarian and don't really have a point, but it sounds like you are basically saying (reusing the above analogy) "Why are we talking about adding seatbelts to cars when we already have helmets?"