The logic here isn't really sound. Fastpass/Maxpass work because they get some portion of the people out of the line. Though the standby wait TIME would get longer - the actual LENGTH of the wait LINE should get shorter.
Think of it this way:
- If you normally have 2000 people going on a ride with no-FP, and the wait time is 45-minutes, it means you have 1500 people standing in line at any one time.
- If you then shift 75% of the queue to MaxPass/FastPass, you now have 1500 people that are going through the Maxpass/FastPass line every hour,but with the wait time with this kept to a maximum of say 10 minutes, only 250 people of these 1500 people per hour would be in line at any point.
- Meanwhile, there still room for 500 people get through the standby line per hour. Even if your standby wait time doubles to 90 minutes, your stand-by line now only has 750 people in it (500 people per hour waiting 90-minutes) instead of 1500 people (2000 people per hour waiting 45 minutes).
So in the above scenario, we went from 1500 people waiting in line at any one point in time, to at most 1000 people waiting in line (250 in MP/FP and 750 in standby), even though the standby wait went from 45-minutes to 90-minutes.
The basics are - FP makes standby people wait in line longer, but because the wait times go up, the actual line length becomes shorter. A great example of this in WDW is in HM - whose queue used to back up out the gates but was rarely more than a 30 minute wait until the instituted FP. Now the waits are often 45 minutes or more, but they rarely back out the gates.