If the total GPA isn’t impressive but there has been an upward trend, an essay about what changed in the applicant’s relationship with school could be an interesting essay - without mentioning grades or ACT. For example, if he spent the early part of high school hanging out with friends from middle school and was reluctant to be part of a high-achieving crowd at high school, why did that change.? If grades fell during a transition from regular classes to honors, why did he decide to take that risk?
No AO wants to read a story of “I am smart but bored/disorganized/ etc.” But any story that helps AOs see who the applicant is today helps put the whole picture together, including a story of growth.