I recommend reading the actual paper. DDG is actually by far the worst by their measures. Even though Google has gotten worse, it’s results are still massively superior to the competition. 9% spam compared to 31% for DDG and 23% for Bing. That’s a huge difference.

I would recommend trying a SearXNG instance if you haven’t before. You can combine results from multiple sources. I use Google as my main source while also having access to the DDG-style !bangs.