Just to encourage further panic (a specialty of mine), I'll run some good ol' FP+ numbers.
The amount of guests per day at MK each day averages out to about 48,000 guests (obviously that number increases during busier times of the year and decreases during slower times). To ease this math, let's assume all 48,000 guests arrive at rope drop and leave at park close and that each guest gets four FP+s for the day.
That would be 48,000 x 4 which would 192,000 needed FP+ slots. Now, let's assume that MK is open from 9am to 9pm (so 12 hours), so now we take the 192,000 and divide it by twelve to get 16,000, so 16,000 FP+ slots are needed per hour.
With the current FP system, there are twelve possible windows each hour

00, :05, :10, :15, :20, :25, :30, :35, :40, :45, :50, :55; occasionally, there will be more but on a day when MK has 45,000 guests, you won't see that happen). Anyways, the 16,000 needed slots in a given hour would then be divided by the 12 possible slots leading to 1,334 (rounding up from 1,333.333) FP+s needing to be distributed of a given slot, park-wide.
Now, here's where the math gets very messy and even more assumptions are made (not like we already haven't made enough). It's obvious, due to demand and capacity differences, Disney won't distribute the same number of FP+s at each attraction (we're going to take parade/firework viewing out of this to simplify things so assume no one chooses the FP+ fireworks/parade viewing options). However, if they were to do that they'd distribute 89 (rounding up from 88.9333) FP+s for one particular slot, because 1,334 divided by 15 (the amount of FP+
attractions at MK during tests) would be 88.9333 and thus would be rounded up to 89.
Taking it further, let's say Disney wanted to increase the amount of FP+s available during a given slot up to 100 (so increasing the amount distributed by 11) for Peter Pan, Space, and Thunder, they'd then have to take away 11 FP+s from less-popular attractions bringing the amount of those available down to 78 per slot. Here's the catch, though: Disney has to take those FP+s away from attractions in the same category or tier, so they can't just take them away from Pirates or PhilharMagic, they need to take those away from Buzz Lightyear's Space Ranger Spin, Enchanted Tales with Belle, Town Square Theater: Meet the Disney Princesses, and Splash Mountain (the last one could be optional as they only need to decrease three). Something similar could be done in the second tier.
Interesting, but a lot of math.