I think it's the scale/capacity of the computer to produce derivative works they're mainly objecting too. Otherwise, as you rightly imply, preventing the copying of style, approach or some other inspiration would kill art stone dead. Or at least mean that the only artists that could survive were those using AI to screen their works against prior art so that they could not be accused of "theft".
One thing I agree with them on is that you should not be allowed to prompt using artists names. That seems unnecessary.