Materia in general serve no purpose and should be removed. The only materia with any degree of relevance towards build customization are Skill Speed and Spell Speed, and even then only for high-performance play and only for specific classes. And they could just simply set a given class's GCD to a specific point and redesign the rotation as needed if it would be a serious problem for them to be set to one specific GCD speed.

The *idea* behind materia (as with item reforging and fiddling with affixes in WoW, Diablo 3, and virtually any other RPG with such a system) is that the player chooses what they want. But that kind of design is mutually exclusive with a balanced high-end raiding/battle system. Players will simply math out which affixes or stats are best and will then proceed to all use the exact same gemming scheme - or they will be inferior.

More than that, though, the proof of how meaningless materia generally are is easy to see by comparing materia loadouts. A tank with Tenacity in every single possible slot is not meaningfully weaker than a tank with recommended BiS gemming - they will still do more than enough DPS to carry their own weight and then some with proper play, so the only difference is if you actually give a damn about fighting for top spots on the FFLogs leaderboards. The same is true for healers with Piety, etc. Even not having the ideal GCD speed for your class doesn't suddenly make them unable to achieve adequate levels of DPS.

Materia basically only matter insofar as you have *something* your class can make use of in every socket, and even then that only matters if you are raiding savages or ultimates - even extremes don't really require you to use materia in order to produce enough DPS to clear, though it might be a little tough if you're doing the brand new even-patch extreme without crafted gear or anything better than last tier's best gear.

Honestly, XIV needs to shift to a horizontal progression system. Their design philosophy is moving more and more towards "as accessible as possible" (which I think is a *good* thing), and that kind of design philosophy tends to be pretty much mutually exclusive with vertical progression systems, as those systems naturally and inevitably gate off content behind grind or performance walls. I guess we're already close enough, though.