we knew it would a) reduce total employment

I have not seen evidence of anyone on Hubski expressing this view. Mostly I see calls for a "living wage" with no clear statement of what that means. In my opinion it is bold to say we "know" anything more than obvious facts like "A change to minimum wage law will affect workers." There are data and theories and predictions and estimates, but little universal agreement.

In my view a reduction in employment after hiking minimum wage is the most likely outcome (though it's hard to say by how much), based on the common sense principle that when stuff costs more, people buy less of it.

and b) help the poorest percentage of the population in the short term

I disagree here. I think it can help some workers (those who will get a higher wage — if we make the rather baseless assumption that employers will not make compensating adjustments outside of salary). It will also hurt some, those who are let go because employers choose not to pay more for labor, and those who would have been hired with the old minimum but now are not hired.

It seems clear to me that the ones who are hurt are likely to be poorer than those who benefit.

Also, those who are hurt lose a lot: their entire salary, an opportunity to improve their skills, a consistent work history, networking opportunities. Those who win only gain a percentage of their salary, and may be expected to work harder or work fewer hours or accept fewer fringe benefits in compensation.

I still want to see what happens

That chart illustrates a good point, which was also demonstrated in the paper kleinbl00 shared. When minimum wage is low compared to average incomes, an increase in minimum wage does not cause much harm. But that is also when it does not do much good either.

if we're going to have a minimum wage it's ridiculous for it to be unindexed to inflation

Either it is a net benefit or a net harm. If it is a benefit, then it makes sense to take measures to prevent dilution of the benefit by inflation. If it is harmful, it should be eliminated; we should not depend on inflation to gradually reduce the damage.

I believe that 500k number was intentionally found using very harsh estimates.

If you could tell me why you believe that it would help me decide if I should believe it too.