He may have become more mature but his skills would have regressed in the college environment. If Lionel Messi had to go through three years of college soccer he'd come out of it as a back bencher on the ARG team at best. But you're using Adu as an example which is again a complete outlier. MLS obviously made a mistake with Adu but the bulk of the blame belongs with Adu, who even recently admitted that he never gave the game the effort he should have. He's barely hanging on to a career in the NASL and he has no one to blame but himself.
Almost as if he's starting from the conclusion that JJ is irreplaceable and then choosing experiments that will support it.