I don't think De Bruyne is a bad move for Napoli. Before anything else, it is a free transfer. And as far as I can see, he has accepted a huge pay cut in his salary as well.
He was earning 24 million euros per year at Manchester City but now it is going to drop down to only 6 million.
Yeah he is more prone to injuries recently but his talent and experience both can still be quite useful.
There's no a better thing than getting KDB as a free agent. They get him with lower salary, while we know how he very experienced player. He's also winning so many PL trophies combined with european trophies. He even won treble. He was earning 24 million euros per year at Manchester City but now it is going to drop down to only 6 million.
Yeah he is more prone to injuries recently but his talent and experience both can still be quite useful.
Earning 6 million still good consider he's not young anymore. He gets 2+1 contract, and that's quite long.
It's a win win situation for him and Napoli. However, his injury prone may be the problem, but i think he's already getting rid of it.
Best of luck him in his new club.