Thunderstorms are impressive, but at their basics, they are just a manifestation of the convective transfer that establishes and maintains the adiabatic lapse, which has been incorporated into climate models for the last fifty years. Convective heat transfer is the cause; thunderstorms are merely a manifestation. That's the way (or much of the way) heat is moved in the atmosphere: by convection.
And, yes, convection is pretty well understood. Your proposal that convection represents a "new" feedback mechanism that atmospheric scientists have never thought about, and that therefore invalidates all the previous models, is a little naïve. In any case, however, precipitation represents 100% humidity. To "invalidate" the feedback effect of humidity, you need to show that humidity decreases with temperature. Saying that thunderstorms increase will, if anything, serve as a demonstration that humidity increased with temperature.