By challenging this one guy, the whole group suffers.
You either be directly unfair and only attack the 70% dodge man, or you attack everybody equally with the potent attacker and kill the other players first.
Aren't you the one saying everyone will have 70% dodge chance by early mid-game?
Also, Feint is a thing, and it doesn't take a murder-machine to Feint successfully, especially against a character who's good at dodging but not so good at swordplay (as most ranged assassin-types tend to be).
And I've rarely seen fights where the group wasn't outnumbered about three to one, so ganging up comes naturally. And there's nothing unfair with intelligent enemies ganging up on the guy they can't hit individually.