CAS is a mission, not an aircraft. And it's not about how close your plane is to the troops, but how close to friendly forces you can safely deliver weapons and how fast you can deliver them. A B-1 circling above the fight dropping smart bombs fits that bill. And 24% is not a majority no matter how you try to twist it. Other aircraft fly the majority of CAS missions.
You maligned Pierre Sprey earlier, and John Boyd by transit, so let's dig a little deeper into the charts, because on their face, they tell us no more than sortie count, and are thus valueless.
More worthwhile metrics might include, for example, some kind of kill efficiency per sortie, or, better, per unit ord used, these often being costly. Another good stat to check would be loss rates or damage rates per sortie. Regarding your Time-to-Target metric, he A-10 was conceived with exceptional loiter capability. Which is quicker to target? A B-1 taking off or an A-10 loitering in vicinity?
The sortie counts are worthless as an indicator of value in-role. Indeed, one could conceivably read them as a simple indicator that insufficent dedicated CAS aircraft are available in the form of the A-10 itself, leading to the misuse of birds like the '16.
Okay, now i'll malign Boyd a little: The F-111, while a horrible fighter, ended up being a pretty good/sophisticated strike/bomber aircraft and Boyd's protege Burton, who ripped the Bradley IFV for the acceptance testing used was unaware of how well suited said vehicle, in large part due to its light weight and mobility, fit into the maneuver warfare doctrine of his old mentor Boyd. God loves irony.
However, this desire to paper over the merits of an excellent CAS-specialized aircraft baffles me. I recognize that the load and range are very similar between the f-16 and A-10, but suspect the increased loiter capability, low-speed manueuverability advantage, and enhanced survivability of the hog make it a better aircraft in the anti-armor role.
I'd add, as a post-thought... those GAU shells are a low-cost mechanism for dispatching vehicles, certainly. OTOH, I wonder about the relative cost issue of maintaining another unique aircraft. Adding F-16s drives you closer to a lower complexity solution in that regard, admittedly.