Name one thing the A-10 can't do in support of ground troops the F-35 can? The A-10 can loiter longer, fly lower, stay on target longer. It can fly from forward unimproved airstrips. It has longer range. It can carry far greater number of missiles and bombs.
So just where is the A-10 deficient in support of ground troops? The F-35 is an expensive fast moving, carries less weapons, can only stay on target for a limited time. The only plane better than the A-10 is the AC-135, and the AC-135 isn't as effective against heavy armor.