The marxist dude is likely cherry picking data to make a bogus point. E.g. the charts in his letter aren't normalized by world population. Pinsker is presenting distributions, not absolute numbers, as world population has a tendency to grow.
He has one valid point. $1.90 might be too low to draw the poverty line. But as the whole distribution has shifted, that point seems moot.
He has another interesting point: People had access to land in the old age, although they didn't have cash. I think that makes sense. Land has some value... but but there's a big cost to utilizing it---it's a full time job :) Anyone can go back... become a farmer, hunter or a herder... live at subsistance-level. I think few people want that lifestyle, as is clear from occupancy stats. The benefits of having access to land and its cost (the specific lifestyle) may cancel each other.