The broad theory is that austerity is necessary for growth - it's a serious theory even if I think it turned out to be wrong with terrible human consequences.

The Reinhart and Rogoff paper was more like factoid of a theory - no complicated model, just a dubious claim that trips off the tongue - "Studies have shown that when debt reach X level, growth tanks"

The thing about this is when the shoddy quality of the study became obvious, people could act that was what drove all the horrible things coming under austerity, as if these weren't the consensus of a large group, study-or-not-study.