traffic and topical fit first" is the whole game right there. DR just tells you the site has some links, it says nothing about whether real people in your niche actually read it. I've had the same thing happen, a cheap link from a small local blog that actually talks about my topic and gets real readers beat out stuff I paid way more for. Google seems to care more about whether the site is actually about your thing and getting clicks than some number a tool made up. The big DR sites are usually just link farms at this point, they'll post anything for money and the readers are all other SEOs. You're basically paying for a number on a screen.

Learned the same lesson with my lawn mower, spent an hour messing with the carb before realizing the spark plug cap just had corrosion. Funny how the cheap fix is always the last thing we try.