You have 100 people in line for a ride. 75 people in the FP Lane. 25 people in the standby line. You move the first 10 people in the standby lane to the FP Lane (increasing the FP volume). The last person in the standby line is now #15 instead of #25. Are you saying his wait is going to dramatically increase assuming the ratio of the entry between FP and standby guests remain the same?
Again you really aren't understanding how this works. You are assuming there are only 100 people, that number of people doesn't change, there is no crowd flow, that they once the 100 are gone there is no one else ie: people continue to line up as those 100 go through the line, and you have no statement of the capacity for the ride, and last but very importantly you are only including ONE ride. In your example this all happens at once, instead of as a function of crowd flows and ride capacity.
I don't have time to go fully into this, have to get to work

But even one simple example of how FP impacts SB wait times.
Ok MOST simple way to explain this ... actually 2 ways.
So a ride with a 100 ride capacity per hour, used to be 75:25 split FP to SB ... you say, move 10 of those people to FPs, wouldn't change wait.
The assumption here is that its the FIRST 10 in line that move to FP, but of course that's not how FP+ works. IF its the last 10 in line, if even 1 of the last 1 in line gets the FP, lines increase for everyone else. Of course, this is more impactful exponentially since we are dealing with rides in the 1000s of people per hour.
Another simple example. OK so 2 rides, one with and one without FPs. You have to understand what the impact of increased FPs means. It means more people in the park. You can be both a physical person, and a virtual person.
Look at any hour, 12 -1. If I have an FP for 12:45. I can go stand in line for another ride at 12, and wait and ride that, and then walk over to my FP, skip the line and ride that. In that sense I am virtually 2 people in the park at the same time. As far as it goes for demand on rides, I actually AM 2 people in the park at the same time.
So 2 rides with I guess 200 people in the park, since we are using simple numbers, each with 100 ride per hour capacity.
Ride 1 - 75% FP, 25% SB
Ride 2 - all SB.
As it was, those 75% people could have been trying to ride Ride 2 WHILE they had reservations for Ride 1 ... already increasing the wait time. Instead of 100 people trying to ride the ride, you have 175 ... giving you an average wait time of 45 mins of wait you now have to disperse between those people. (please please please understand this is not a real wait time, this would assume no load time, no spacing between rides, perfect crowd flow, etc.) So you went from 0 wait to a 30 second wait average per person. Of course this isn't how it plays out, that wait actually builds exponentially as people arrive and the line backs up.
Now Increase the ratio, to 85% FP and 15% SB. Instead of 75 people being able to wait for ride 2 while they have a virtual person in line at ride 1, its now 85. You now have 51 mins of wait time to disperse, instead of 45.
This says nothing about the impact of crowd flows, multiple overlaps, multiple FP bookings, the disincentive of SB lines, etc.
But increasing the number of available FPs naturally increases the wait times of rides because it increases the total number of people (though some are virtual) in the park, and changes the ride/demand dynamics.
Hope I made this clear enough. LT was much better at explaining this.
And again, this has no impact as long as you are well below capacity, but its impact increases the closer you come to hitting capacity, that's when you have the overflow demand that has to be soaked up somehow.