The famed Media Bias Chart - which is widely circulated in the news media and social media as a well researched, broad analysis of the news media - has labeled the Daily Kos as a "Hyper-Partisan" outlet that presents "incomplete stories, unfair persuasion". The Media Bias Chart's in-depth methodology is readily available online, and is generally well regarded. Kos manages to be in the worst half of this category - barely above the worst category of "news", which the chart labels as propaganda that is damaging to public discourse. Sites in the lowest category - which Kos is in danger of falling into in the future, include Breitbart, NaturalNews (an anti-vaccine alternative medicine site), and Infowars. The Daily Kos is placed in the same category as the Drudge Report, The New York Post, the Daily Mail, and is actually ranked lower within that category than the Federalist and Buzzfeed News.
When you would be better off going to freaking Buzzfeed for your news than Daily Kos, you know the website has no real worth. Someone who spends all of their time on Kos will be extremely ill-informed. This confirms my own experience on the site - where essentially only party-line, pro-DNC, Liberal Democratic points of view were embraced. The occasional Progressive Dem or Moderate could sneak in, but only if they did not too aggressively defend their viewpoints.
Daily Kos is an echo chamber by design.