In raids and trials its usually pretty easy to notice if someone isn't pulling their weight. Generally one of two situations would arise. Either the content is trivally easy (Camp Westwind) at which point many wouldn't care much since the duty will be done very quickly anyway or the content would actually be challenging (EX battles) in which case the person not pulling their wait will stand out potentially to the point of causing the duty to fail and probably get themselves kicked from the duty for being lazy.
Further statistic board don't tell much about the performance of your group. For a start not all dps can bring the same level of damage (BRD dps is quite a bit lower than say a BLM) and further statistics don't really tell you how well a player had handled the mechanics, just how much damage they pulled out. I had a BLM in a Good King Moggle Mog fight who was pulling much bigger numbers than me on my bard. Ironically them just Auto attacking would be better since they fixated on Moggle Mog and kept triggering his ultimate while the adds were still up, wiping the raid party. After 5 wipes we just duty kicked the guy since s/he wasn't listening about switching to adds and complete the duty easily in one go.