In 2k19 Speed and Speed with Ball are the same rates of movement. For example a player sprinting with 80 speed will move at the same speed as a player sprinting with the ball at 80 speed with ball. Weight does not negatively affect your speed outside of the obvious drop in speed and speed with ball ratings. A 270 lb player with 80 speed runs at the same rate as a 180 lb player with 80 speed. This holds true for speed with ball as well.
Only the acceleration stat affects how quickly your player gets up to top speed. Speed rating and weight have no impact. However, the difference between 70 acceleration and 80 acceleration, for example, is very small. We would not recommend making your acceleration rating a huge priority.
Once again, only the lateral quickness rating has any affect on how quickly you move side to side.