A mobile QB can be nightmare to defend in the NFL, but the player must be a dual threat with an NFL arm. Mohomes in KC and Trubisky in Chicago are young QB's who give defense's fits because they can beat you with both their arm and their legs. Guys like Lamar Jackson and Tim Tebow, though, who do not scare any defense with their arms don't work in the NFL, though, for the reasons you listed. It will be interesting to see if Mohomes and Trubisky can stay healthy, though. Watson in Houston is already getting beat up, as has Cam Newton in Carolina. The Chargers had already faced the Jackson-led Baltimore offense a few weeks earlier, so they were able to devise a scheme that completely shut down the Ravens until LA inexplicably went into a prevent defense.