Enhance soil or start over
6 years ago I put in 3 dwarf apples (Bud 9 stock)suited for NC (local grower). My soil is hard / dry clay, so I added some additional organic stuff in the hole, and plenty of mulch. Fertilized decently, 6 hrs direct sun daily. The 3 are still "sticks", little growth, no apples, few blooms. This is the only sunny spot in the yard. Some posts suggest it doesn't take great soil. I know from digging other holes it is incredibly hard clay, no rocks, likely fill from roadbed. Even grass is hard to grow. Other trees in yard are giant oaks & hickory which seem to have no problem.
Idea is to wait till dormant, dig them out, change it to raised bed in same area, or at least dig to a sufficient depth with a tiller and not replace all the soil, but make it more 50-50. Is this a bad idea? May consider new healthy starters..