While I can appreciate people wanting something similar to the system for FFXI BLUs, it simply just wouldn't work for FFXIV. By having swappable skills, there will always be a meta of skills that are "essential", and if you have to grind to get those skills, why would a group choose to take a Blue Mage, who perhaps needs time and aid to get the "correct" skill set up, when they could swap to a different tank? By imposing these limitations on Blue Mages and Blue Mages only, you effectively limit their player base and usability to only the most dedicated players. And at that point, what's the point in having them in the game?

That's why I chose to have the skills be obtained in job quests, rather than grinding in the world. That way, narratively speaking, you still get the experience of going out and getting the skills from these monsters, but from a gameplay mechanic, they are on parity with the other jobs without needing excessive amounts of extra work.