Materia's IV are overrated, overpriced and a complete bait. You can do a perfectly fine Novus without a single materia IV. There's this ridiculous perception that you are not optimizing your weapon if you bump 3 stats on it, but it's just that, a silly perception.

SCH - 21 Piety, 21 Det, 33 Crit
WHM - 21 Piety, 21 Det, 33 SS
DRG/MNK/BRD - 21 Det, 21 Acc, 33 Crit
PLD/WAR - 33 Parry, 33 Acc, 9 Det

And bam, you have a Novus that costs 100k so gil is not an issue anymore.
Having 10 Crit instead of say 10 accuracy means your character has like 0.8% more critical hit chance, yes, not even 1%, you are paying 5-7 millions for a 0.8% more critical hit chance, which by the way doesn't come for free because you are trading it for 10 points of accuracy that could avoid you having to eat food every time you step onto endgame.