We can call him mobile if you prefer. I'm not sure there's a clear line between mobile and "dual threat". In my mind, a dual threat is just someone who can make things happen as a runner when the passing game breaks down. But if the standard is that you have to be "dangerous" at both, then I think there are very few dual threats in the league, period. You're basically looking at Hurts, Allen, Jackson, and MAYBE a couple others. Someone like Fields, for example, is a very capable runner, but has just OK passing stats, and is definitely nowhere near the passer that Mahomes is. Does that mean that Fields is not a dual threat because he's not an elite passer? The standard goes both ways.