I (21f) am 5'5" and skinny. I recently attended a self-defense class, and there I was tought how to use a pocket knife. And as I have some male friends 6'5"+ tall, I thought that that height actually makes their belly particularly vulnerable in case of a fight (compared to a short guy/girl):
- a short person's shoulder height is around the same level as the the tall person's belly making it easier to stab/hit;
- a tall guy's belly is proportionally a larger target.
And in general, if a 6'5"+ guy stands in front of me with his stomach released (even if he has just a bit of a belly) it feels like having an exposed, large and squishy punching/stabbing bag right in front of me, into which, if needed, I can easily harshly and deeply plunge anything straight away.
I also practice historical fencing (rapier) and most of the times I stab tall opponents into the belly - my favorite thrusts are ducking counterattacks when I duck while they attack, go low and impale a tall guy's unprotected belly right onto my rapier.
I disagree with your opinion. I think being the shorter person in a fight is generally a disadvantage.
All else equal, the person who is taller will likely have more mass, and thus have more muscle to utilize against you. They’ll also have a bigger wingspan, so their zone of threat is bigger.
When I used to study martial arts, my instructors always used to say “don’t bring anything to a street fight that you don’t want taken away and used against you”. Unless you have the element of surprise, and are using a knife that’s attached to your body, welding a knife against someone bigger may backfire. Being a master of de-escalation tends to have a better mortality rate ;)