@hermitboi
Hero kid knows the mc's power but hides it for the sake of the party's harmony.
This scene happened differently in the WN, the hero actually chokes the dumb muscle head until he almost fainted.
Then in the internal monologue of the hero, it was explained that every time the hero wanted to defend the MC, he was stopped by the MC. The other members are needed by the party since they are the strongest. The party couldn't advance with only the hero and a black mage, so MC decided to lay low.
He laid too low in my opinion, thus this all happened.