This!
In the FP- era, I seldom got more than 2 or 3 fast passes, only got them when needed, and used them strategically.
Now, you virtually must book 3 FPs in advance. Since everyone is doing so, and with 70-90% of capacity being used to service those FPs, there is no such thing as a fast standby line anymore.
I'm guessing that the average visitor, still visiting the average amount of rides, still spends a similar overall amount of time in line.
Maybe they previously waited in a bunch of 10-30 minute lines, now they are doing 3 FPS, and a bunch of 20-50 minute lines.
If I previously would do Haunted Mansion with a 10-20 minute wait... But now, it is either "instant" with FP for 70% of guests, but 30-50 minutes for standby.... Is more being gained or lost?
The "old days"... In moderate crowds, might have 3-5 bad lines during mid-day. But even without FPs, there were another dozen attractions you could enjoy without significant lines. Now... It's 10+ attractions that have the bad lines, and very few that can be enjoyed without a FP or significant line.
And if 70% of capacity is going to FP, with 3 FPs per person, and most FPs gone by lunch.... How many attractions are people really enjoying? Seems to my math, people are probably only doing 5-7 attractions in Magic Kingdom. Use your 3 FPs, see a show/parade/fireworks, do 1 or 2 low/no line attractions (Hall of Presidents, Carousel of Progress), and maybe bear 1 or 2 of the long standby lines.
I wonder if FP+ has actually increased the number of attractions that an average guest experiences.