It depends very much on what the small, weak, and short person knows and what the big, tall, and strong person doesn't.
I do not mean this in a negative way, but you are showing your lack of understanding of martial arts. Good technique and body mechanics overcome much.
My own style of karate comes from Okinawa. The Okinawans are not large people. The founder of my style was maybe 125 pounds soaking wet. And yet he trained US Marines who were are large as 6 foot 8 tall and weighed 250 or more, most of it muscle. If he could not demonstrate the effectiveness of his technique to them, convince them that he could toss them around like rag dolls, do you suppose they would have trained hard with him after work, night after night, and brought his style back to the USA with them? He obviously had to prove how well his system worked or they'd have refused to train with him.
Big is nice. I'm big. It means very little by itself in martial arts. If you don't already know that, you're not very good at martial arts.
You think so, but it's not true. We have a young woman in our dojo who most likely weighs about 100 pounds if that. I am pretty sure she can kick most men's butts. And even assuming someone larger got ahold of her and threw her to the ground, she'd be back up in a second, and they'd be tasting their testicles. Trust me on this.