You really don't know, do you?
A number of CMs who work the "merge point" between FastPass and Standby lines have reported that the ratio gets as high as 10-to-1 for some of the popular, low capacity attractions.
There's a reason attractions such as Soarin' and Toy Story Mania frequently have 2-hour waits even when the parks are not particularly crowded.
It's why I'm now of the opinion that WDW would be a better place if they completely eliminated FP/FP+.
A ratio being 10/1 has nothing to do with the percent of ride capacity taken up by FP. They are two *entirely*s, different things. Plus, that's a kind of obnoxious response "your really don't know, do you".
You are confusing ride capacity and demand. Let's say a ride has a capacity of 2,000/hr. If you give out half the capacity FP (1,000) per hour, that leaves half for standby. If in the first hour, 2,000 standby riders show up, then you have a 1-hr wait.
Normally, you'd expect a FP wait time to be about 0 (that's the whole idea, isn't it), but if everyone shows up right at the beginning of a window, there will be some irregularity. In the example above, there will be no riders waiting on the FP line, and 1,000 riders on standby. Technically that's a ratio of infinity, but say for the sake of argument that a lot of FP riders show up at once and there are 50 on line. That's a ratio of 20-to-1 on line. But still only 50% of the ride's capacity have been reserved for FP.
If the real demand for the ride is 3,000 riders that hour (as it is in the example above - 1,000 for FP riders, and 2,000 arriving as standby), and there is no FP, then 2,000 riders will be serviced the first hour, and 1,000 will be left on line - the same as if there were FP.
One could argue that not having FP would reduce the demand, and therefore the line would be shorter. That's true. So let's suppose that the lack of FP reduces the demand from 3,000 to 2,500, then you have 1/2 hour wait at the end of the hour, and 500 riders who were so unhappy with the wait times that they didn't get to ride at all. I don't see how this improves the situation.
No matter how you cut it up, FP=good, and lack of FP does *not* reduce wait times, except if you consider riders who gave up in frustration.