Not such an out of reach thing, since the Cubs (White Stockings at the time) existed prior to that particular association's founding... and there were only 9 teams in the league. The Cubs even left the league for 2 years due to the Great Fire of 1871, returning in 1874. Oh, and in 1871, ALL of the teams were new to the league, as it was a new league. Several teams from the old leagues lost many of their players, as they did not want to transfer to the new league and it's different rules. The White Stockings were the only team to transfer from one league to the other in 1871 and not lose any of their players.
The Cubs began playing as a semi-professional unit in 1870, but have roots as far back as 1866 as an amateur squad. Most of the guys that were around in 1868 as amateurs were on the club that won the NAPBBP pennant in 1871 (hence why they were considered a semi-pro team, they still had more amateurs than pros). They weren't considered a full-time professional team until 1876 when the National League started up. At that time, the White Stockings went out and signed the premiere players from the defunct NAPBBP and NABBP (two different leagues, as the NAPBBP formed due to a split with the NABBP over rules and regulations disagreements) to become the dominant team in the new league.
So, it's not quite the same kind of story to claim the Cubs won a pennant after just 1 year of existence... and stating that the Marlins took 5 years (against 27 and 29 established teams... not 8 unestablished teams). Also, the Marlins have actually won the WS twice in the past 20 years, the Cubs have not. They even beat the Cubs on their way to one of those WS victories. Considering that the Cubs dramatically shift gears after Spalding sold the club to Wrigley... and even more shifting when Wrigley sold the club to the Tribune.... you can say that the Cubs are not the same organization they were in the 1870s. Over the past 20 years, the Marlins have been overall a better organization simply due to the 2 WS wins compared to the Cubs' 104-year drought.