We literally have not. We have tested low-altitude, low-saturation, continuous maritime dispersal.
You can go look up the differences in dissipation dynamics between that and what’s being proposed by the BS in Econ student and his growth marketing cofounder.
I don't now who the BS in econ student you're referring to is, as it's not the context of the article. We have had massive SO2 emissions from past stratovolcano eruptions.
Sure - there is definitely some gap between these natural processes and the artificial processes being proposed, but it is a narrow enough gap that it does preclude a fair number of second-order effects, compared to almost all geoengineering ideas that do not have such natural experiment equivalents.
You can go look up the differences in dissipation dynamics between that and what’s being proposed by the BS in Econ student and his growth marketing cofounder.