Regardless of what people like to say, size in general, does make a difference in a fight. That doesn't mean a larger person will always win a fight. But it's an advantage just as being faster, more agile, better endurance, more skill, etc are all advantages.
When people act like size makes no difference in a real fight, that is sort of like saying speed doesn't matter. Or strength doesn't matter... but of course they matter. But, the person who will most likely win will be the person who has a better distribution of all of these "advantages".
When you learn martial arts, you'll need to know how to defend and attack against all different shapes and sizes. Tall people will need to know what techniques work against shorter people and likewise, shorter people will need to know and work on techniques that will work on people taller than them. Most martial arts will employ a wide variety of techniques and you'll need to use the right tool for the situation.
You are looking for the simple answer and guarantees when there is no simple answer or guarantee. It is always about skill.
The bigger they are, the harder they fall.
No.
