ACT/SAT is clearly more important, But unless you are literally studying for the test all the time, you should be able to do both. My son did. He had time to work on his CFA, even though he played varsity sports throughout the entire year, was President of NHS, and studied to improve his ACT scores. I helped with his CFA workouts, and it was great bonding, and a good escape from academics. He also had a pull-up bar in his bedroom door, and did pull-ups whenever he had time. Same with push-ups and sit-ups. Those things take only a few minutes. He would do 2 1/2 mile runs typically when he got home from practice. That stuff is good for your mind and soul, in addition to helping your CFA score.
This issue gets debated frequently, and I argue the CFA is very important, and there is clearly a difference between an average CFA score and an excellent CFA, just as there is a difference between a 28 ACT and a 32 ACT. If academics are worth 60% of the total WCS, and that is split between ACT and class rank (30% each) then each sub-score on the ACT is worth less than 8% of the WCS. Would you think that Math or English, science or reading sections on the ACT are not worth working on? Each is worth less on the WCS. In a close call between candidates competing for a spot a 2% difference between candidates might be a very big deal. And I think frequently there are several competitive candidates competing for one spot.