Critics have also stated that the computer-adaptive method of placing more weight on the first several questions is biased against test takers who typically perform poorly at the beginning of a test due to stress or confusion before becoming more comfortable as the exam continues.  On the other hand, standard fixed-form tests could equally be said to be "biased" against students with less testing stamina since they would need to be approximately twice the length of an equivalent computer adaptive test to obtain a similar level of precision. 
During the course of the argument essay you will need to demonstrate your ability to write well, but more importantly you need to demonstrate your ability to dissect an argument, which further gives evidence of your skill as a discerning reader. Just as in the issue essay, there is more than one "right" answer. What matters most is that you demonstrate your ability to intelligently respond to an argument. You need to show that you can critique the provided statement, and you'll need to point out specific details and fragments in the provided snipped of text that you think support your claims. It is these skills that the GRE test takers are looking for.