Is this level of retaliation too cruel, too merciful or just right?

So, in this novel, the protagonist and his entourage ran into an arrogant young master and his entourage.

The protagonist was a low-key kinda guy, but he was the nephew of the emperor. The arrogant young master was just the son of some city lord.

So anyway, they got into a verbal argument about who has the right of way and the arrogant young master ended up saying, "I am going to kill you, your parents, your grandparents and everyone in your clan!"

And then, he saw the protagonist's maid and decided to have her. So he ordered his soldiers to arrest everyone except the maid. Well, he said "arrest" but he also told his soldiers to kill anyone who resist. Except for the maid, of course.

In the end, the protagonist's bodyguards defeated the soldiers. And the protagonist beat up the arrogant young master and crippled the latter's dantian.

Now, if you know the xianxia/wuxia/xuanhuan genre, you will know that crippling one's dantian is equivalent to crippling one's future.

So, considering what happened between the protagonist and arrogant young master, was the protagonist's retaliation justified or not?