As someone else who is short and skinny, this is a very dangerous assumption. I’ve trained in judo, karate, and wrestling, and gotten in a couple actual fights, so have some experience here. In a real fight for your life being shorter is a disadvantage, even more so if you have average length arms for your height. It’s possible to overcome that disadvantage if you are more skilled than the opponent, but assuming equal skill you are likely to lose.

In an actual fight, going for a gut stab with a knife is one of the worst options you have. It means you are absolutely within grapple range, have done almost nothing to hinder their mobility, and even if it is eventually fatal, it often takes a very long time to die from a gut wound. You would be much better either going for a hit that would instantly kill them, or aiming for somewhere that would hinder their mobility enough for you to escape.

Also, in the real world it doesn’t work like fencing, no one is going to break the fight up as soon as you score a hit. If you want to actually prepare for a fight you should try out a sport that doesn’t break on point scoring. In general boxing, MMA, or wrestling would be a better option to prepare for a real fight that doesn’t get broken up.