@chrightt they said they're fine with players not being able to reach all the content. Evil demons won't probably be able to reach max lvl in fireball. So some other players not being able to get something because of immunities should be fine as well.
About high resistance - in my book it's worse then immunity because it might make impossible to kill for you - damage output too low vs mob damage output and he simply kills you - and that's where "nerf qq" starts. Because the game tells you that you can kill everything with a single skill and then it turns out it's not really true. With immunity - reasonable immunity - you know that sometimes you have to do something else. I'll use @Jetah argument and say - worst case hire bodyguards
And about anime and mmo - it's not a good argument as they are usually nonsense unfortunately I'm pretty sure most mmo manga authors didn't play mmo at all.