Um, I wouldn't call any of this arguing for the nonexistence of social hierarchies. More like arguing that hierarchies are unstable, context-dependent and, well, social.

If all of the IT workers decided to quit, what would happen to the poor workers? They'd still pick food, and they'd be fine.

Ah, but once the IT workers invent food-picking robots, poor people are screwed.

If all the poor workers stopped picking food, what would happen? It will spoil, and the IT people won't eat.

They can always eat whatever the striking food-pickers eat (and will win the competition to get it, if there's a scarcity problem). As a side-question, what does a food-picking job actually entail? (I'm not a native speaker)

The IT-workers vs food-pickers example doesn't really hold up very well and even if it did it wouldn't be an argument for the nonexistence of social hierarchies except under very narrow and artificial definitions of the word 'hierarchy'.

Different people are treated differently. Some are deferred to more than others. Some are regarded with suspicion more than others. Those differences tend to be stable over time within a given group. That's your social hierarchy. That those relations are different in different groups, that they can change rapidly in unusual circumstances and that ultimately they are determined by the contents of human minds doesn't mean they aren't a real phenomenon.