My buddy was in the rangers pre 2001. He said the rangers were mostly using optics on their rifles even then.
Makes sense to me, Since the rangers being part of SOCOM. If you were issued a rifle with a Aimpoint CCO with flip up irons.. You would of course be more familiar with the CCO.
My other buddy which Graduated Infantry school recently said when he was issued his M4 in basic it came with a Aimpoint CCO with it and he never had to zero his irons.