The old Fastpass system required you to go visit a kiosk near the ride itself, and acquire a ticket for a specific time window later in the day, at which point you could go in via a shorter priority line. It worked great and was actually kind of fun.
I understand they would want to get rid of the physical passes the machine printed out as the machines were probably maintenance nightmares, but they did more than that. They changed the system entirely to an app, which is fine in itself, but they eliminated the need to visit the ride area to get the pass, which is part of what made the system fair. Instead, you can schedule the passes ahead of time, even for future days, and of course passholders and people staying at the park get priority, so all the popular rides' Fastpasses are already gone by the time the typical visitor is even able to attempt to schedule anything, which means they will just have to wait in the regular long line because there's no way smooth out the demand across the day anymore, since all the scheduling happens for a select group ahead of time without requiring any physical commitment.
In short, they sabotaged themselves, at least from this visitor's POV. Fastpass was one of my favorite bits of visiting Disney parks, but the new system is one of my LEAST favorite bits. Ah well.