Everybody agrees that AB5 is flawed and needs more work. But Prop 22 let money-losing, worker-exploiting companies literally write the law they wanted and made sure nobody could change it. A referendum on AB5 would have forced discussion and improvement. This closes that off.
For better or worse, this is the system working as intended. The point of the proposition system is to let the people pass laws the legislature refuses to. It would be pointless if the legislature could overturn or gut propositions with a simple majority vote.
All the other statute initiative propositions on the CA ballot this year included a lower threshold than Prop 22 (ranging from 51% to 75%).
However, none of them (including Prop 22) allow the legislature to overturn it even if they achieve the threshold - only to modify "in furtherance of the original purposes" of the proposition.
AB5 passed with 80% of the vote, so requiring a lower threshold would be self-defeating.
Prop 13 is the landmark example of a ballot initiative that set super-majority thresholds for legislature. In it's case, the ability to create new taxes-- a property which has been specifically (and unsuccessfully) litigated against: https://www.latimes.com/opinion/la-xpm-2011-dec-26-la-oe-new...