The numbers are based on the % of inquiry numbers being thrown around are per 'type' of play (ie being "in the pocket" has had more injuries per play than designed QB runs). "Running" QBs (and all QBs) are injured at a higher % on non-running plays. For example, Cam Newton's first big injury was trying to make a tackle on an interception. RGIII got injured trying to recover a fumble.
There's a narrative that 'running' QBs take hits that take a toll over their careers, but there's very little data on that because Pocket Passers have generally been the prevalence and there have been very few "elite" running QBs over the history of the game to really have a comparison compared to pocket passers who are promising then flame out.
I think this is a confused take because RGIII just wasn't a good QB. He made up for that by running, but by getting injured (in the pocket recovering a fumble) he remove his ability to make plays running and then couldn't pass well enough. It's hard to argue that he had been in the league (and college) long enough for the 'hits to accumulate' making his body weaker. He just wasn't a complete player.
I'd also suppose that age is much more dangerous to running QBs than the 'hits' they take running the ball.
That said, I'm 100% on board with limiting the designed runs. I think they're stupid, but because of the 'injury risk', but because I believe Allen is more dangerous with his arm and 'option' to scramble if it breaks down on most plays.