There's probably generally a much smaller percentage of park Express Pass riders than park Fast Pass riders. I don't go during the busy season, just with moderate crowds, but usually there's only a handful of people going through Express, while Disney's Fast Pass lines are heavily filled with people. We've rarely had Express pass waits more than 5 or 10 minutes, and most often they're just about walk ons. Disney's Fast Pass lines get really lengthy at times.....I don't think it's fair to compare the two systems since they are different animals.
Totally true, they are different systems. Disney's is just flawed. Nobody will debate the fact when FP first launched, wait times went up quite a bit for most rides. Wait times continue to rise as the parks see more and more people visit every year. Frozen has made that VERY clear. The fact that they have to shut down the standby line after a long downtime so they can let the THOUSANDS of people with FP+ times that were missed, is an issue. Having 5 minutes inbetween return times is an issue. While highly unlikely, you could have almost an entire hour's worth of people show up at one time making the standby line stop for 30+ minutes. If they give out 50 FP+ every 5 minutes, that 600 people an hour, over half of the rides capacity. It's a major flaw in the system.
Universal tried the paper FP style system shortly after Disney started. They quickly noticed that it has a more negative impact than positive for all guests, so they changed their system. When the standby line doesn't move for 10 minutes because of to many FP guests, standby people get upset. With Frozen, if you don't secure your FP+ 30-60 days in advance, there is a chance you might not even be able to wait in a standby line, which is a huge issue that is sure to upset guests.
Even with Universal giving their three top tier hotel guests UNLIMITED express, AP holders express after 4pm, and allowing guests to purchase express, the lines rarely become a major issue. When I have express, it's odd to have to wait more than 5 minutes. Normally there is only a few people in the express queue.
I would love to see what would happen if Disney dropped the return times for a week or two. Keep the whole system the same, but just remove the times. If a ride normally gives out 5,000 FP all day, still give out those 5,000. Post Standby and FP wait times at the entrance to the rides. This way, if a FP wait time is say 30 minutes compared to the 60 of standby, maybe a guest will go do something else and come back later. Don't place a priority on the FP line. Switch between the two evenly. All 5,000 FP's are not going to show up at once, and if they do, a lot of them will go do something else since they are not stuck in a time frame. Other guests will race to the park at opening, use all three right at the start, and not have many options for a 4th or 5th FP that day, removing a decent chunk of FP's in the early hours when the lines are generally not an issue.
Ultimately though, I see the system changing again down the line. First will be limiting it to just on-site hotel guests and AP holders. Maybe they will sell it for off-site guests. That will weed out some. If that doesn't work, remove it from the value hotels for free and offer it for a reduced price vs. off site guests. This should help fix the wait times for both FP and standby.