Opponent is the misleading word in the question.
Some people disagreed, opposing would be drastic, on the conclusion but that does not mean that they cannot have overlapping lines of reasoning, which is highlighted in e.
However if final choice is not with the publisher,one cannot say anything about the argument as the Passage never explicitly states that the publisher chooses the cover! Thus for b to be correct,one has to extraneously assume that the new publisher was responsible for the change in cover and not any of the say content contributors of the magazine.so one cannot be absolutely sure of the premise that leads to b.in short for b to be an assumption ,it has to have another assumption which will not make b an infallible one ,hence incorrect.
But e is more certain and immediate. Hence e.