You are categorically wrong in almost every respect on the subject of knives.

Knives are lethal when used with anything approaching skill.

It is this simple. You take a utility knife or a $1 steak knife. You hold it in your dominant hand with your thumb on the spine of the knife. You thrust towards the left hand side of your victim's chest, about level with the breastbone.

Bonus points if you orient your knife horizontally so it won't get hung up on their ribs.

A knife with a decent, non slip, ergonomic handle (like a $1 steak knife) is a bonus, because you hand is less likely to slip along the blade and cut your fingers, allowing you to stab more than once. A Buck 110 Hunter (arguably the most popular pocket knife of all time with 15 million made since 1963) would be great for this. A knife with a hand-guard or hilt would be better, but it doesn't really matter because one decent stab is fatal even if you cut your fingers.

Knives kill by causing bleeding. Any forceful stab to the chest or gut is a mortal wound, but hitting a major blood vessel is required to ensure your victim dies before surgery.

"Oh, that is so complicated" You say. Who would know how to do that?

Everyone. Everyone who has spent more than ten minutes holding a knife knows how to do this.

The authors report that stab injuries were recorded most frequently in the chest, followed by the abdomen and then the neck

From

An evaluation of human stabbing performance to inform the standardisation of textile damage examinations: Do simulation trials correlate to reported stabbings?

Which includes a meta study of stab wounds reported at Australian hospitals.

This is the way knives are actually used in the wild when people actually intend to kill someone.

Slashing or hacking is relatively ineffective and more likely to result in superficial wounds, and this is fucking obvious to anyone who has thought about it.

How do I know all this? I have spent years working in security, and getting stabbed is something that keeps me up at night. If someone pulls a knife you run because even a total idiot can kill you.