Precisely why there are weight brackets to try and mitigate this.

Doesn't matter how good you can swing a sword, if you can't deflect (let alone stop) the force of a proper swing of someone far stronger than you, who also has adequate training, it generally won't matter if you're better trained when they push right through your defence like it was papier-mâché. You need to have the strength to rightfully match your opponent, and no amount of bullshit from shows like Game of Thrones where a little girl with a dagger kills a warrior king will change that reality. Can it happen? Sure. Will it consistently happen? Absolutely not. You can't get by on exceptions when it comes to fighting. Only so many times you get lucky pulling stunts like that before someone comes along and knows that trick and you get destroyed as a result. Doesn't matter what fighting technique or discipline is used, whether it be fists, swords, or even guns.