Eh, your topic is wrong, there is no fallacy in refusing customization, the fallacy is in not understanding the complexity of creating content for PVE based on all the variables you offer to PVE without alienating certain job setups from the game.

So ya, Frost Mage, Fire Mage, Thunder Mage "specialization" for Black mage, then what Alexander might make it impossible for Thunder mage to work because of certain concepts so those mages get shun from content or they are forced to change their "customization" into something else. Would you honestly call that system customization when a player is forced to change their skill setup because of the metagame and alienation being thrown at them?

That's why customization isn't as good as people might think it is, they think oh options, oh the illusion of choice sign me up. But at the end of the day the "choices" you make are pretty much set in stone based on what the community says is acceptable and if you choose otherwise then be prepared to be left out of a lot of content.