and at whose expense?

If you think anarchy is some kind of substantial deterrent to an underclass when we're talking about the same people with functionally the same underlying morality that create and enforce them in democratic systems, I have a bridge you can barter for. More equal e.g. economic systems can thrive under democracy; democracy is not the problem.

for how many?

Difficult to quantify given it's difficult if not impossible to decouple life-changing advances in quality of living from the nations and systems that facilitated them. For how many, though, compared to before? For near-basically everyone. Life is still unbelievably shit in major swaths of the world, and yet human life overall is still improving in most areas, still has obvious room for betterment, and is still markedly better than before. There's still plenty of Return to Eros shit we need to fix and C-suites to jail, but we obviously can fix it under democracy. We of course have minimal data for actual anarchy, which leaves a convenient argument from ignorance for anarchists to cling onto.

I guess what I was getting at earlier, come to think of it, is a subtype of the argument from ignorance. "Well we've just never tried it, which is why it's way better than this thing that's tested and has problems."