Being called a top player and he won’t start doesn’t mesh. Quality instruction and practice reps are important. But the real test of improvement and development is on the field.
It does appear leaving his current situation is the right move. A motivated player shouldn’t be around players who lack motivation and accept losing.
My recommendation would be something in the middle. Leave the existing situation. Get in the best coaching and instruction environment where he can start.
If you can’t find something in the middle take the new situation as long as he will get on the field a reasonable amount of the time. If it doesn’t work out at least it’s competitive and he will get exposure and you will see potential solutions with other competitive programs for the following year.
Good luck.