The same as above, but the stats are applied through actual Materia. Each job can select up to 5 materia and spend any amount on each. But, since it's actual materia now, we should go a little further. For instance, we might create a few classes of these.
Common would be your plain secondary stats: Haste, Determination, Critical Hit, etc.
Rare might be limited to just 1 or 2 and might feature things like the ability to self-raise or to offer an additional charge to Swiftcast, Bloodbath, Second Wind, etc.
Because these would be situational and either actively cast or conditional, they might not even take on AP themselves, but simply drain AP from the materia slotted below them upon use / if used. In that way, they come at cost, temporarily draining from one's dump-stat Materia with the amount trickling back to the drained Materia over time.
Finally,
Epic grade of materia that we might take only one of and which is specific to one's job in order to offer some simple change in power that nonetheless varies one's rotation at some scale.
For instance, reducing the damage of Twin Snakes and Dragon Kick themselves in order to increase the modifier of Twin Snakes would allow for one to drop Twin Snakes before DK and TwS and thereby allow for different optimal GCD thresholds. By supporting only a few of these, with very simple rules in themselves despite decently pervasive rotational effects, the devs can allow for tweaks to playflow for jobs that would otherwise just barely fail to attract certain players without creating new balancing nightmares.