Touring Plans did a study comparing wait times for all rides before/after FP+. Spaceship Earth, Pirates, and other rides that got FP like Journey Into Imagination or rides that have more people using FP like DINOSAUR went up significantly.
Here’s one factor everyone forgets. At the same time they switched over to FP+, they also did away with the GAC and replaced it with DAS. I was working attractions at this time, and months and months leading up to the GAC going away, we were tracking their usage - We had clickers counting the number of guests coming through the FP line every hour. It’s been so long now, I don’t remember the actual percentage, but I remember that number being in the double digits. I want to say it was as much as 20% of the FP line was GACs some hours because back then, they were unlimited usage, and no matter your opinion of GACs, they were most definitely being abused.
Disney knew that if the FP+ was going to work, they had to curtail that abuse, thus they switched to the DAS. They increased the number of FPs given out per day, but they significantly cut down the number of people using the disability service by limiting rerides and making them wait for return times. The waits may not have increased despite the number of FPs increasing, but they would have most definitely had they not simultaneously eliminated a significant amount of abuse that was happening with the GAC. Basically increase of one and the decrease of the other cancelled each other out, hence there not being significant differences. Except in the rides that didn’t before have FPs at all, which mostly all increased, if I remember correctly.