Warden rekt Kensei! DEUS VEULT

Did I notice his sword can break through a samurai's armor?

Not exactly historically accurate if it can just punch thru armor...

Maybe it depends who forge these swords. Just like in Forged by Fire

Even a perfectly made sword isn't going to punch thru plate armor. That's what blunt trauma weapons like maces and warhammers are for.

Durability and weight are important not only the sharpness. I agree too. Heavy weapons are built to break through the armor. One hit of a mace will dent the helmet and fracture your skull or chance the helmet dent can kill you

Btw, is it possible for hidden knives to work on stealth missions?

Depends. You would have to be very discreet, and be prepared to face weapons much heavier than your own. Daggers would probably be a better choice.

We should take care of the heavy fighters because they carry heavy weapons which makes their attack slow which is easy to evade and kill. Facing a Warhammer soldier can die easily by being stabbed in the neck

Actually, even heavy weapons can be used with surprising nimbleness. The trick is to close in where they can't use the superior mass of their weapon to the fullest extent. Look up "scholagladtoria smallsword vs zweihander" for further information.

Your right! Heavy fighters can be fast when they wield Zweihanders like Siegfried from Soul Calibur or Cloud Strife of Final Fantasy. If you have good physical strength you can wield heavy weapons easily and swing them fast that you can kill a ninja or Assassin.