FPs result in long, slow moving stand by lines.
I understand both sides BUT your point isn't valid. FP does have a significant impact on guests who want flexibility of no FP. You can make the case for FP, you shouldn't make the false claim on the effect on guests who don't use it.
You don't see a difference between picking a park and picking what attractions you want reserve and at what time?
You want a win win. Limit fp to maybe 25% of ride capacity. Charge enough $$$ for the FP so guests who want them can get them without having to reserve them months in advance.