It's not just that DDG is good enough - it seems that DDG has better results than Google for many searches. Any topic where Google engineers and their algorithms believe they know better than you will return "worse" results. I believe they are weighting results by some measure of truth-value for a particular type of information, and this is bad for a couple reasons. First, they might get the measure of truth wrong, either out of ignorance or conflict of interest. Second, you might want a more literal search where the keywords match exactly even though the info might not be very accurate, for instance if you were researching alternate theories.
Examples of where Google search fails to return relevant results because they know better than you are medical, political, illicit/illegal, conspiracy theory, and famous people. Often times the first page of results don't contain the keywords and don't seem to have anything to do with your search query, whereas DDG results do.