If best way is the only...why do we see different setups ?

[Yukiko]

Try to fullequip one job and then try same with 2 others...
Most players already switched tank away from PLD, same with healers and DPS...
You will see that after a few more months because weekly caps its not as if you can switch class within one day!

[Reynhart]

Most players already switched tank away from PLD, same with healers and DPS...

Most of the tanks who switched from PLD thinking they'd clear Savage still failed for months before succeeding...that is to say, far far after having a PLD wasn't an issue anymore.

They just did that "because the elite said so", without realizing that it's not because they had the best setup, but because they are the best players.

True. However, when you do the encounters a couple of weeks later (better gear and what not), it does not mean the "best" way isn't best anymore.

I'm not saying it's not the best, I'm just saying that it doesn't matter.
In regards to customization, it's not because the elite players will find the best build for any job that the vast majority (emphasis on vast) will have no issue whatsoever playing and enjoying their character with a more peculiar build.