According to physics, because global warming lowers the differences between any two areas, there should be less storms and those storms should be less severe.
Not between any two areas, but between average tropical and average arctic conditions.
In the standard global warming scenario, the arctic gets much warmer, particularly at night, while the tropics remain about the same as now.
As you say, this reduces the delta-T between these two regions, which is the primary driver of world weather. Just not the only one.