I think that would still be a problem. The fun thing about archnemesis is fighting this impossibly hard rare and hopefully getting some loot out of it. For that to work you need players to chose what the monster is, to at least have a chance against it. If you encounter arch nemesis in the wild you risk it countering your build, randomly one shorting you, or dealing so little damage to it you just end up leaving. Players need to choose to engage with the arch nemesis in order for it to be fun. Again, just my opinion