I agree with the previous poster he does lack a bit of lateral quickness. It's the same as speed. You see it mostly when he attempts to go upfield after the catch - the reason why he doesn't usually get past the first defender, aside from not being one of those big bodied receivers like Landry, is that he is changing direction, the defender squares him up, and he's just not quick enough when he has to change direction to get to either side of the defender and is easily tackled by the legs.Lack of lateral quickness? It's the way they are using him. It's not that hard to understand.
Of course I think that if the Dolphins were able to generate more spacing to their offense he'd have more chances to catch the ball and continue going at speed, which he does have. But you have to think that when the team organized their draft strategy to get him where they did, and when they schemed so many plays that required him to stop and start like that, that they thought he could pick up where he left off in YAC in college. I mean, a bubble screen to a guy who doesn't have lateral quickness is pretty much a wasted play, since the whole point of the play is the get the DB to charge and then make him miss, opening up the space behind him for a 10ish yard gain, but bubble screens we've run with Waddle this year have been wasted plays.