That graphic is based on number of stores. Based on sales, Chick-fil-A is number 3 with only 2.5K stores. Based on sales per store, Chick-fil-A is number one by a wide margin. Their per-store sales are more than 4X that of KFC and that gap widens every year. Even when ranked against the big sit-down chains like BJs and Cheesecake Factory, Chick-fil-A is number 5. And this is for a fast-food chain that's closed on Sunday and frequently embroiled in political controversy!
It's been kinda crazy to watch that chain grow so fast. Our grandkids eat Chick-fil-A probably 3-4 times per week (pre-pandemic). If DW and I take them on an outing, that's the only place they want to go.
The drive-thru typically has two-lanes, each of which holds probably 20-30 cars. Employees holding tablets take your order and money when you get about half way through the line.
To me, the food is sort-of average, although I never seem to mind batting clean-up for the grandkids. I remember them back in the 1980s as a little hole-in-the-wall at the Mall that nobody went to. How it became the sensation that it is today is a mystery to me.