Suppose an optimum set of unarmed tactics against a skilled puncher gets you a 90% chance of success, but an optimum set of unarmed tactics against a knife-wielding attacker gets you only a 30% chance of success.
Now suppose martial art A cuts out a bunch of techniques that are effective against a puncher, but dangerous to try against an attacker with a knife. (clinching, covering like a boxer, etc). That might drop art A's effectiveness vs a skilled puncher down to 50%, while leaving its effectiveness vs the knife at 30%.
Meanwhile, martial art B keeps all those techniques and thus manages 90% effectiveness against a puncher, but success against the knife drops down to 10%.
This gives you a situation where martial art A is superior for knife defense, art B is superior for punch defense, but A still has a higher success against the punch than against the knife