The % is the percentile, the closest to 100 it is, the better. TECHNICALLY, 50% is the average, but anyone with a true understanding of their job will be around 75+. THAT BEING SAID, it is extremely gear dependent. You being at 14% doe NOT mean you "suck". On FFlog, you are mostly competing with people who are (or very close) to BiS gears. So that is important to keep in mind.

The info it does tell you tough is if you are improving and if you personally need a bit of work. After taking a quick peek at your gear, it's not optimal (you should definitely try to upgrade that i255 weapon), but you should technically be able to get higher. The next step is to figure out what you can improve; take a look at that Ravana fight, figure out your buff. Did you have grease lightning always up? how did you manage internal release? All those things can be seen on the interface of that particular fight.

You can send me a private message if you want more specific explanations.