I was gonna say that was too bland to be it's true form... Of course a party formed on the basis of "distrust" wouldn't be able to handle it immediately
It might be okay in this case because it seems to be from a super rare and special variant from the regular unique quest that no one happened upon, considering it involved the unique monster to activate
I like how the manga didn't do some bullshit like "The MC beat the OP Legendary enemy on his first attempt because that's totally how video games work!" thing