That's not grammatically incorrect. They are asking you to either agree or disagree, then providing you with multiple choice answers which either agree or disagree with the statement provided.

"My character felt powerful."

- not at all (statement of strong disagreement)

- slightly (statement of slight disagreement)

- somewhat (neutral)

- quite a bit (statement of slight agreement)

- very much (statement of strong agreement)

There is no confusion about what the statement "not at all" would indicate, in context, versus the statement "very much."

edit: The only problem that would arise is if they had asked, "On a scale of 1 to 5, how much do you agree or disagree with the following statements?" because they have not set the parameters of what 1 is meant to indicate, and what 5 is meant to indicate. Here, though, you know that a 1 is "not at all," and 5 is "very much," so there is no ambiguity.

-Travail.

Seems like you're being pedantic to me. Regardless of the semantics, you said it yourself:

These sort of details go right over my head. I understand that a human being wrote the survey, and us mere mortals make mistakes.

Still you are looking at the wrong thing.

You see:

Please indicate how much you agree or disagree with the following:

not at all

slightly

somewhat

quite a bit

very much

---------------

I see:

Please indicate how much you agree or disagree with the following:

I was able create a character I liked.

The look of my items and clothing allowed me to stand out.

I was satisfied by my class choice.

I was satisfied by my race choice.

Then I see

not at all

slightly

somewhat

quite a bit

very much

Understand?