The 1855 Classification System was commissioned by Napoleon III for the 1855 Paris Expo fair. Napoleon III wanted to introduce French wines in a way that would not confuse visitors. He wanted a ranking system so people would be able to easily identify the best wines in France.
He passed this task to the Bordeaux Chamber of Commerce who then passed this task to the Syndicate of Courtiers, which was an association of wine brokers/negociants.
Back in 1855, the wine trade was controlled by these wine brokers/negociants who decided what would be sold to consumers. They ranked the wines (mostly of the Medoc region, the centre of the French wine trade) based on reputation and trading price of the wines. The system was never meant to be a rank of quality although quality and consistency did play a large part in building the reputation of the wine and what it sold for. Just like in 1855, even today, the Classification System is still very important to the wine auction and investment market as it still, by and large, is representative of the reputation and price of the wines. No matter how high the rating, I rarely see Cru Bourgeous or non growth wines of the Left Bank at auction but every growth wine, no matter how obscure, will command a price at auction.
There were originally 58 wineries that were given Growth status. Through splits of wineries, now there are 60 Growth wines. in the following levels:
1st growth: 5
2nd growth: 14
3rd growth: 14
4th growth: 10
5th growth: 18
Dubignon was taken over by Malescot St. Exupery so if you drink Malescot, that counts as drinking 2 growth wines.
There have only been 2 wine changes in status since 1855 and by and large, over the 150 year period, the Growth system continues to hold true with respect to pricing and reputation.
So while it is interesting and consumers need to be aware of this system, it is not a system that tells you the quality level of the wine, especially at the lower rungs of the classification system. It does tell you which wines people value at auction, which does affect consumer pricing of wines. That is why there is a disconnect between consumer preferences and the 1855 Classification System: because it was never meant to be used by consumers and never meant to be an absolute signal of quality.
It is still important to taste the growth wines. Because of globalization, none of these wineries are in danger of having a shortage of money or resources and consequently, all the growth wines are of good quality. They each have rich histories dating back well before 1855 and because essentially all Trophy Wines on the Left Bank are growth wines, if you want to drink Bordeaux Trophy Wines, like it or not, there is no way around drinking and understanding the Growth System.
Langoa Barton is a 3rd growth.