1991 is the demarcation year of the Atlanta Braves: worst-to-first and then excellence thereafter. 15 years of excellence. 2006 was when it all fell apart: not only did the Braves fail to win their division for the first time since 1990 (insert 1994 asterisk here) they fell below 0.500 for the first time: 79 wins and 83 losses.
That said, they played a little better than that. They were one of only three teams in franchise history to finish below 0.500 with a Pythagorean projection above 0.500. (The other two were the 1951 Boston team and the eternally perplexing [to me] 1973 squad.