Why "als" here? I would have expected "sowohl gut und auch schlect" for both good and (also) bad.
Maybe it's because it can be translated as "as" - as in... "The person is both good as well as bad."
according to dict.cc, "sowohl ... als auch ..." means "both ... and ..."
i may be mistaken, but is not the idea here that they are as good as they are bad?
No. The translation "The person is both good and bad." is correct.
If you want to say "The person is as good as he is bad", you'd say "Die Person ist so gut, wie sie schlecht ist.".
I think it also may have the meaning of "the person is as good as is bad", after all these two sentences have similiar meaning i.e. that the person is good and bad at the same time.
Or you could also say "Die Person ist genauso gut wie schlecht"