When I mention 41+ taking more time, I am including all endgame activity as well. Materia is an active system even at capped level, and the focus of it isn't primarily for leveling.

That being said, it is also in part a form of customization. A way to make your gear your own with your choice of melds even at lower levels. As far as expected use goes, however, as suggested by the devs and Yoshida directyl, endgame content is balanced around players having gear with stats that equate to a single high tier meld on everything. For that reason we can understand that most of the Materia system's merit comes at higher and capped levels.

That is the reason the system is so top-heavy, because it is being balanced in such a way. Most of the confusion comes from both tier IIIs and IVs being 41+. People naturally expect it to all be spread out- which is what I feel is more like what sounds sensible on paper- but in fact by design tier IVs exist to essentially be rare and more potent versions of tier IIIs, while lower tiers exist to add customization to lower levels.