How are ocular dominance columns monocular despite binocular complex cells?
Ocular dominance columns are not purely monocular, nor are simple cells purely monocular.

Simple and complex cells both exhibit a range of ocular preference, from preferring one to the other. See this figure from Hubel and Wiesel, 1962:



Hubel, D. H., &amp; Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. The Journal of physiology, 160(1), 106-154.