I agree, but I suspect this was also what was believed when they originally did it and adversaries found very clever ways to find that cookie store - that part

I agree, but I suspect this was also what was believed when they originally did it and adversaries found very clever ways to find that cookie store - that part at least is true, which is why I bother mentioning it, given the complexity of browsers it is likely very daunting to redesign this kind of thing around the existing features. Anyways, I'm glad I'm not working on browsers, it seems like an ever-losing cat and mouse.