On the other hand that lesson has been learned over and over again. Ground attack planes from the IL-2, To A-1, SU-25 and A-10 has one thing in common, they were designed to work low and slow. It inevidably leads to casualties but a slow, well armoured plane still is more effective than a fast fighter. U dont go low and slow unless u can go really low and slow. Using F-35 for CAS will lead to casualties, it will fall victim to AAA just as often as the A-10. Down low u are not that helped by stealth technology.