Mat Zo just called out the big names who use ghost producers
Dennis Waakop Reijers and Tiesto is old news, hell I remember in an interview Tiesto said that "Tiesto is really just the band name for Tijs and Dennis who is the master behind the scenes" or something like that. In Armins Imagine documentary I think he also shows how his tracks are produced, He writes and produces the "skeleton" of the track then Benno comes in and finishes it and makes it listenable, so it's probably like 50/50 there.

It's where Ghost writers become uncredited where it's complete bullshit.