If true, it's very disappointing to hear this.
I do find it very hard to believe that not a single CM directed you to first aid or that no guests offered aid if your son's leg was "stuck" under the ride. One thing that Disney takes very seriously is safety of guests.
One other tip is that when you are vacationing at Disney in the summer you always need ponchos. That would have at least mitigated some of the issues with the rain and being soaking wet. Generally speaking, most outdoor rides only shut down if there is lightning within a certain radius of WDW, rain itself does not shut down rides. We rode Slinky Dog Dash in the rain a few weeks ago. The parks can still be enjoyable in the rain, you just need to be prepared to deal with the weather.