Actually, this in anecdotal, but i believe most of the cases where ddg lets me down are when the query is VERY specific. More general searches seem to have no diff between google and ddg results.
This is my intuition as well. As soon as the query gets too specific, I'll just tack on a "!g".
This is precisely my approach. I’m an engineer so sometimes need to make very esoteric searches, but I’ve been using DDG for coming up on 10y.