Gut loading may also be an issue, feeder fish are probably malnurished themselves, and crickets need to be gutloaded with a high quality food that contains calcium for 24 hours before fdeeding otherwise they are about as good as a potato chip. Honestly that could explain the small frog size.
You will get much better growth with nightcrawlers, dubia and pacman food. Pacman food is somewhere around 43 percent protein i believe, crickets are more like 21 percent and the meat to shell ratio is lower compared to dubia. Dubia also have a high available protein percentage as well.