No I don't think that fire
No I don't think that fire would be a weakness. If you had driven at 100mph through a concrete wall and hit a tree with a gasoline car, I would expect not only a fire, but fatalities. That a Model S did this and caught fire, but the occupants were unscathed is a testament to its safety. In two cases where Model S drove over large pieces of metal debris and yet the car warned them to pull over and get out, and they did even retrieving items from the glove box before the fire began is more than I expect other cars would have done. It might even be that if such large metal debris on the roadway had hit a gasoline car, even if it did not hit a fuel line or the gas tank which would have ignited a fire, it might have pierced the under carriage and hurt an occupant of the car.