Thing is, every single strong one in the show, would be fairly invicible even without nen or other supernatural powers. Why? because they have the wits, some have experience etc.
Then they also happen to have incredible powers they can play with.
However, they also have flaws and weaknesses.

Something different about that show is that bad guys aren't necessarilly all that evil, like good ones aren't pure and saints.
Bad guys aren't dumb or totally fucked up in the head (well maybe Hisoka is... )
The troupe is great as even if they are incredibly strong as individuals, they still are able to work together as a group.
Even if that coop is limited, it clearly increases their efficiency.

Kurapika can't defeat them as a group right now, he'll have to wait for other people to kill some or to be able to team with others.