You asked about my friend with big upper body, heavy squater, but thin legs. It seemed like genetics with him. Try squating heavy before giving up. Old routine is one set of squats per workout. one set of 20.
Do 20 reps no matter how long it takes you, rest without putting weight down if you have to. Each leg day add weight, even if it is only 2 and half lbs., then 20 again. Before you know it you will be squating heavy.