Emphasis on the word secondary. That usually amounts to one or two points of difference. That you have a player who put an 18 in his Int rather than the stats that directly influence his every attack and damage roll is, frankly, bizarre--at least if you're holding that out as an example of decision made for the sake of effectiveness (and if you're not, then it's rather a moot point).
The warlock in my party did. He ties for highest AC of the party when he shadow walks, and his diabolic grasps sling people 5 squares away!