Cinderace's best stat is speed, followed by attack. Brave nature lowers speed and raises attack. Really, your Cinderace could afford to lose a little speed if it means raising attack. While in some ways, brave isn't the best, it's better than modest or something. However, you should switch the nature to adamant with nature mints ASAP, since you'll definitely be running a physical set on a Cinderace, and then you won't need SpAtk.