I have the feeling SE doesn't want every job to be competitive and perfectly equals at very high levels of play. They just want every job to be viable and capable of clearing content, and have jobs that are better for different kind of contents (which is not the case of every MMO btw, e.g. I came from Wakfu, where there's like 18 different classes but 6 or 7 of them are just incompatible with endgame).

Some jobs are the best during progression, such as DRK, WHM and RDM.
Some jobs are the best at speedkill runs, like NIN, DRG, BRD, AST, WAR.
Some jobs are the best for casual content, like BLM and SAM (which can actually speedrun a dungeon for example, or bring very high damage for 24-players raids where everyone is running over the place like headless chickens).

That's only my opinion on the matter though.