You most certainly could do two. But Bama chooses to do only one with the other 3 OOC teams barely having a pluse. And I hate it! I long for schedules like 1977-78. Years in which Bama had their NC given to ND ('77) and won the NC ('78). So what you are proposing can and has been done by Bama without jeopardizing the ultimate goals.
In 1977 Bama's OOC opponents were; at Nebraska, at Southern Cal, Louisville, and Miami (Florida). In 1978 they were; Nebraska, at Missouri, Southern Cal, at Washington, and Virginia Tech.
In 1977 Bama and ND lost only one game. Both on the road on the same day. Bama at Nebraska, and ND to Ole Miss in Jackson. The same Ole Miss that Bama had beaten by 3 TDs the week before in B'ham. In 1978 Bama lost only to Southern Cal.