> Walmart's presence lowered the living costs of low income families by $1k-$2k

These studies are useless in isolation. If the super-optimisation of production and supply chains (less factory workers, drivers, other lower skilled labour) and moving production to lower cost economies (far, far less factory jobs) also reduced the average income, then the benefits are far less clear, and may disappear altogether.

Nothing happens in a vacuum. If the people who are supposedly benefiting from these low prices are the same people who lost their jobs to the MNCs in the first place, I doubt they're feeling all that grateful.