First, how about defining "tough"?
Secondly, I have been to "tough" enduros. One that comes to mind is Train Robbers. Here, they had a finish for the kids/women at 21 miles, and the terrain was appropriate for the riders considering the area. I say considering, because when you point the truck to central Arkansas you should expect hills, rocks, and creeks everywhere. Don't expect groomed grass fairways. If this is too tough for you,then consider a different event. The C loop was shorter than the A/B as expected, but the terrain is the terrain.
Third, the subject of speed averages being high is a whiner's delight. Different clubs have different philosophies. Some try to let the C riders zero half the checks on the short course if they can keep time (15 and 18 MPH averages in fairly easy terrain), others take points from everybody starting at 3.1 miles. You can only ride so fast, dictated by your ability, not by the promoter. I have been to enduros where the winner and second place were separated by 6 seconds on tiebreakers and each dropped only one point. It is possible this event was decided not by riding ability, rather the 6 second difference could have occured based on an Emergency check in a 15 or 18 section. I have also been to events where the overall winner dropped 28 points under ideal conditions (temp/moisture/dust).
As a C rider, if you drop 5 points or 50 points, the speed averages have no real impact on your score. If you ride over your head and crash, that is not the fault of the promoter. Even the top guys have to manage their own personal fitness relative to the terrain, keep it upright, and ride smart.
Qualifier-style enduros, like they run in MI and the Red River enduro in TX, have all known controls. Why bother even having a test section if it does not contribute to the overall outcome of the event? They will try to take points from the top guys at all the checkouts in this style event, so the B and C riders will drop points too.
BTW C riders, the higher speed averages do provide a benefit for you that you may not have considered. If for example the club has several 15 and 18 sections, the fast guys behind you that are riding possibles will be passing you MULTIPLE times per mile in these sections. You'll be doing your best to ride the average, and they blow by at 25 mph and pull over, then repeat over and over in the section trying to zero (30 seconds into the minute) an unknown E check. With higher speed averages they pass you once early on in the section and you don't see then again until after the next longer reset or gas stop.
Having promoted bicycle events in the past and involved in our club's enduro, I can tell you that every course is the same and has the same problems: It's too long; It's too short; it's too easy; it's too hard; it's too short; it's too long; it's too rough; it's too sandy; it's marked too well; it's marked poorly; etc, etc, etc.
The promoters/organizing clubs have spent hundreds of man hours preparing for the event. They know the terrain and what the weather does to it, and if you get a bunch of rain that might make sections unridable they will do their best to route around them. Changing the course at the last minute is more work than most people think as it effects all the mileage after that point. More than one re-route can create a timing nightmare, plus alot of upset people at the rider's meeting who programmed their computers the night before off the route sheet on the Internet.
Go ride and have fun, thank the check workers and hosting volunteers profusely, and find a local club to contribute to the sport with your time. Your perspective might change if you see it from the other side.