I'll certainly agree with #3 in general being less well answered by DDG. It seems to me to be mostly with compound terms and having to manually use +'s and "'s to enforce terms.

Given there's no tracking (feels a bit odd saying that nowadays with any kind of seriousness), do they monitor which queries people use !g for, and try to optimize their engine for these?

One feature I do like though (I'm not sure if Google etc offer this nowadays), is they'll often provide the top-answered StackOverflow answer in response to a query above the search results. That has proven handy a fair few times, esp. for some of the shorter answers (e.g. arcane command lines, git invocations etc).