And I've been using DDG for a bit now and have found it perfectly useable.
That's great that you use DDG and find it useful! If Google was a true monopoly, as the current media blitz would have you believe, then you would not have been able to so easily switch to DDG (or Bing, or...).
This is shady, at best. It probably contributes to the US’ current political instability (different propaganda / news in red states), and is also probably an unauthorized use of personal information in places like Europe that have laws about such things.
I can't say with confidence how far along Google is toward the threshold of "Monopoly" and have yet to hear an analysis that I would consider definitive in any way.