Most of savage and extreme fights have mechanics called "DPS checks" and "Enrage". If the party isn't dealing enough damage, it will result in a wipe. These filthy damage meters allows us to know what is our actual DPS, and so, to improve. If we deal more damage, the fight is shorter, and so, easier (less mechanics to deal with).

So, if you don't know how much damage you are dealing, how can you improve ? What you suggest is to just get better gear, melds or food to progress, but practice and knowledge of the class is also a very big factor in your DPS. And loving a class does not prevent you from playing it poorly, no matter good your gear is.

Now, BLM's purpose is, and is only destruction. BLM's kit is only raw damage. It brings nothing to the party except damage and an AoE limit break. So, if damage is the only purpose of BLM, why shouldn't we measure how much damage a BLM is actually dealing ?