His range is nothing special, even on his dash attack. Learn the timing of your attacks (you should be getting fairly comfortable if you've been playing a fair amount since... yesterday =P) as well as the timing of his dash attack, its quick, but it doesn't mean you can't react to it =) Once you have the timing, just use your awesome range advantage, not with Latch necessarily, but grab or Fsmash/Dsmash. You wont be able to get a ton of damage from latch because of MK's ease removing them, but he has very little range on his attacks and poor KO moves, so exploit that.
You should be living easily to 180% + on FD if your DIing well, so just put in the effort to really watch his attacks, and react/anticipate correctly to make use of the range advantage. Its just like baseball, sure a fastball isn't easy to hit at first cause its moving fast. But after 20 fastballs, if you think about and learn from the first 19, you know how fast to expect it, and can then anticipate the speed and swing at the correct time. Theres a lot of characters, but to be good at SSBB we're going to have to learn the timing on just about all of their moves =) fortunately playing more will help you do this naturally, give it time, but if a single move is beating you, especially a small range quick move like MK's dash, just really put effort into learning the timing.
-True