The 737’s speed and position on approach to MIA were largely determined by ATC and the traffic in front of it. An extra 400lb of weight would make a measurable difference in many parameters if you cared enough to measure it, but it’s not going to change it enough to alter the planes place in line with Miami approach.
Even setting aside that there are many small factors affecting aircraft performance, this isn’t a case of sensitive dependence on initial conditions. There are a number of step functions (ie ATC) that substantially reign in small variations. This isn’t newtonian ballistics