I would say the weakest World Series loser in recent times may have been the 2007 Colorado Rockies, although they did pull off a ridiculous win streak to get in to the playoffs.
The Cardinals have had some terrible teams win the World Series. The 2006 team won 83 games.
The 2011 team won 90 games.. I only remember that 2011 team because I went to visit PNC Park (Pittsburgh)in July that year. A lovely stadium. The Cardinals made the most mental / fundamental errors I had ever seen a ball team make. I pulled up the box score
St. Louis Cardinals at Pittsburgh Pirates Box Score, July 24, 2011 | Baseball-Reference.com
Just looking at the box score I saw the Cardinals had 3 errors, were picked off twice, gave up multiple steals (one where I remember nobody covered second base), hit into a few double plays. It was a total crapshow. Looking at the boxscore they were 53-48 at the time -- I was stunned to see them in the World Series that year based on what I saw that day.