It’s worse than all that. A 3.0 at his current school may be a perfectly respectable GPA, one that at the very least reflects competence and the ability to handle tough work. If he changes schools, his transcript will still say 3.0, but if the other school is easier a 3.0 might raise questions about his basic competence.
Sure, a careful reader, if he or she is familiar with both schools, shouldn’t make that mistake. But you would be putting a lot of faith in the system if you trusted that his application would be studied with enough attention and expertise to reach the right conclusion. What’s more, if his application were studied with that much attention and expertise, any bump in grades after the transfer would be significantly discounted. It’s not likely you can win this game.