Chaos resist on Chthonic Bloodletter and any bosses that shares the same model

Is there any reason these mobs having an insane chaos resist of 118%!? Especially consider Chaos RR is the hardest in the game to come by.

I understand cold/vit or Aether resist on some other bosses since you can actually get 100%+ RR against them, but Chaos unless you go for a very specific build or set its going to be hard to slog against these things.

Chaos RR is gradually getting better. It has always required gear to get decent amounts. Though any character has access to Eldritch fire + Manticore which is ~60, symbol of solael is another 10 so it is bearable until gear is accessed. Demo+inqui have their respective RR skills too.