Let me use some hypothetical numbers to illustrate why more people with FPs does not necessarily mean longer waits in the FP line.
Soarin is a good example because FPs there were always fully distributed. As soon as the park opened the FP return times would move out quickly until the FPs ran out, often by early afternoon. If more people are using FPs than before at Soarin, that can only mean that they are distributing more per hour. So, let's say, for example, that Soarin has a capacity of 1500 people per hour, and before they issued 1000 FPs per hour, devoting 2/3 of the capacity to FP holders. Now if they increase that to 1200 FPs per hour, but devote 80% of the capacity to FPs they will still be able to accommodate all of those people in an hour and the FP wait would be the same, with fluctuations based on how those people return.
That would obviously mean that fewer people per hour would be admitted from the standby line. If the standby wait has actually gone down slightly, that would mean that a standby wait of 60 minutes translates into fewer people standing in that line than when a higher percentage of capacity is devoted to standby.
My experience and observation has been that this is what is happening at several of the rides that used to have FP+. The FP waits are not longer than they used to be because the standby line is being held longer to accommodate guests with FPs.