Charles the "prequel" used his time as Prince of Wales to develop a persona of his own, make connections and establish his own very substantial legacy, not to mention doing things the monarch would not be allowed to do.
Even Edward VII, who was allowed to do almost nothing and was known for decades as a playboy and womanizer, still managed to become expert in networking, PR, and international relations, all of which he put to good use in a still-memorable nine-year reign.
If Frederik can't utilize his time as Crown Prince equally wisely, why would he suddenly become more efficacious with a crown on his head? If he can't, then it just might be his fault, and not his blind, selfish, unfeeling mother's.
As this is heading straight back to "The Future of the Danish Monarchy", that's all I'll say.