Hey! You're a horsey person! My daughter's do Hunter Jumper. Here's a pic of my oldest at a champ show a year ago. That same champ show is next week, but her horse is lame.

He should be fine, but not in time for the show.
I think people underestimate the physical ability needed to ride a horse.
Yes, description of terrain can really vary from one person to another. That's why I mention feet of elevation climbed a lot and, sometimes, grade of incline. In my century, the "big climb" of Torrey Pines was about 2 miles of 7% grade. That, with other climbing resulted in 3000 feet total. There's a climb here that is maybe a quarter mile at 13%. That's stupid steep! And REALLY slows down your average pace.
I have ALSO found that when the terrain is literally "rolling", I can go a lot faster. I rode in Tahoe a couple of months ago and was able to sprint up a short rolling hill having just come down a previous one. Did this over and over again and really boosted my pace. That was almost 1400 feet of climbing. Doing that same amount of climbing here, where I might climb the entire 1400 at once or split into two climbs, yet not starting from a downhill roll ... gives me a completely different and slower pace.