The Materia system isn't really about customizing, it's about empowering. It was mentioned by the devs that Materia is used to bring the strength of lower tier gear up closer to the strength of the next tier of gear; it creates a middle ground that makes progression smoother, and the stat caps just further that aim by keeping the gear balanced in the position they're aiming for it to be.

It's not about making your gear work in a particular, special way, just about making it work better at what it already does.