Lower iLvl gear better than higher iLlv?

[VarHyid]

Ever since I was a sprout, whenever I searched for information about gear, any info I found always started with "item level is the primary factor in determining the item's stats" so higher number = better item, right?

Now that I'm in the endgame, I noticed the following:

Augmented Cryptlurker's Mesail of Casting (iLVL 530):

+427 Vitality
+413 Intelligence
+211 Spell Speed
+301 Direct Hit Rate

2 materia slots, "Advanced Melding Forbidden"

Total: 1 352 points + 120 materia = 1 472

Law's Order Helm of Casting (iLVL 510):

+375 Vitality
+372 Intelligence
+288 Spell Speed
+202 Determination

5 materia slots!

Total: 1 237 points + 300 materia = 1 537

Although the base stats are indeed lower on the i510 gear, thanks to the 5 materia slots, you can get 65 more points on this peace of gear. Maybe not much, but it adds up if you do it with the whole set.

That said, am I missing something? Is the lower iLVL gear actually better stat-wise than the higher one and this whole "just look at the item level" advice I've heard all the time only applies to lower levels where it's a simple indicator of what's "better"?