So you'd like to see the F-35 trying to mow down Ruskie tank columns trying to break through the Fulda Gap after air superiority had been achieved? That was the environment that the A-10 was designed to handle. The A-10 was designed to be a flying tank because it was meant to fly low and take enemy AA fire. Its air defense capabilities are really only useful against attack helicopters.
The F-35 can't take the beating that an A-10 would shrug off but it's unlikely to receive such a beating. In an anti-armor role the F-35 isn't going to do low and slow strafing runs with its guns and doesn't need keep its boresight on target to hit with its air-to-ground missiles. In the CAS role the F-35 has a much longer range, higher speed, and longer loiter time than the A-10. It can deliver precision guided munitions much faster than the A-10 and then scamper off to the next target.
The F-35 is also capable of carrying more combat payload than the A-10. It can carry more munitions faster and farther than the A-10, all with low observability (depending on payload configuration obviously). When it returns from a CAS or strike mission it can also re-arm and fly CAP.
The A-10 is a nice plane and obviously very survivable. Its replacement however does not need to have all of the exact same characteristics to perform the same tasks.