I’m willing to accept that Just a Flesh Wound only reduces damage for Black Knight by design, and not for his shared allies when his team is under shared damage.
It may not be what I would have expected, but tbh I don’t think it holds his team back by much either. It does make Wilbur + tile damage an interesting way to counter him; though I’d argue his defense being so high makes this less of an issue with shared damage, and his berserk attack boost makes this significantly risky for the attacker too.