This. While I agree with fusional that we may be a bit "job Idea" obsessed--or at least, I certainly am--a bit more love on the developer's part of the diversity in the "idea" of a class definitely seems a better solution than every player being quicker to turn to the new best-of-patch situational class-stack.
I don't see why Paladins can't follow paths other than the sword-and-holy-board defender. I would like that a really good Ninja who has adapted his character to be the absolute best at certain types of tanking could outdo a paladin in those specific instances. On the same token, I don't see why a Paladin can't make one hell of a hard-line push offense with key bonuses usable against undead, empowering from light elements and additional damage vs. dark element enemies, etc (without being situation-locked to those types).
Any balancing tension from patch to patch comes first from the rigidity given to the jobs by their original development, even if player biases may ingrain these distinctions later. In either case, this "take it or leave it" mentality is not ideal (this job will work for this and never for that, so just level a Warrior, BLM, and MNK already). I don't know why people are oft to treat it like the bread and butter of (online gaming) life, when there are choices other than grain for this already optional meal. Better design is possible.