Nex and Geb had each INT 30 by the end of their mutual war. They didn’t solve the puzzle of Azlant’s IOUN stones… partially because they did not find and prioritize enough diamonds to also gain Wisdom 27. And partially because there is more to thinkoomph than Intelligence and Wisdom and Splendour, such as Golarion’s spells readily do enhance; there is a spark to inventing notions like probability theory or computation or logical decision theory from scratch, that is not directly measured by Detect Thoughts nor by tests of legible ability at using existing math. (Keltham has slightly above-average intelligence for dath ilan, reflectivity well below average, and an ordinary amount of that spark.)
But most of all, Nex and Geb didn’t solve IOUN stones because they didn’t come from a culture that had already developed digital computation and analog signal processing. Or on an even deeper level—because those concepts can’t really be that hard at INT 30, even if your WIS is much lower and you are missing some sparks—they didn’t come from a culture which said that inventing things like that is what the Very Smart People are supposed to do with their lives, nor that Very Smart People are supposed to recheck what their society told them were the most important problems to solve.
Nex and Geb came from a culture which said that incredibly smart wizards were supposed to become all-powerful and conquer their rivals; and invent new signature spells that would be named after them forever after; and build mighty wizard-towers, and raise armies, and stabilize impressively large demiplanes; and fight minor gods, and surpass them; and not, particularly, question society’s priorities for wizards. Nobody ever told Nex or Geb that it was their responsibility to be smarter than the society they grew up in, or use their intelligence better than common wisdom said to use it. They were not prompted to look in the direction of analog signal processing; and, more importantly in the end, were not prompted to meta-look around for better directions to look, or taught any eld-honed art of meta-looking.
Modest spoilers for planecrash (Book 9 -- null action act II).